desktop-pc-hardware-guide

before you open it

• Shut down, switch the power supply off at the back, then press the power button once. That empties the capacitors: the board LED goes out.
• Touch the bare metal of the case before you touch anything inside, and again now and then. Do not work on carpet in socks.
• Take a photo of the cabling before you unplug anything. It answers every question you will have in twenty minutes.
• Screws go into a cup or onto a magnetic tray, not onto the desk.
• Never force a plug. Every power and data connector in a PC is keyed and goes in one way: if it resists, it is the wrong one or the wrong way round.

it does not start: the short list

Most PCs that "died" after a move, a cleaning or an upgrade have one of these. Go through them in order before you suspect a part.

1. The switch on the power supply, and the power cord at both ends.
2. The 8-pin CPU power plug near the processor. Forgotten or half in, the fans spin and nothing else happens.
3. Memory: take the modules out and push them back in until both clips snap. Then try with one module only.
4. The monitor cable is in the graphics card, not in the mainboard socket above it.
5. The monitor is set to the right input.
6. Reset the BIOS settings (see below).
7. Listen and look: beeps from the small speaker, or four small LEDs on the board labelled CPU, DRAM, VGA, BOOT. The one that stays lit names the stage that failed.

The same as a guided path with questions: the troubleshooting wizard, tree "the PC does not start".

memory: which slots

• Two modules belong in the second and fourth slot counted from the processor, usually named A2 and B2. That gives dual channel, which matters most for integrated graphics.
• Push straight down on both ends until both clips close. It needs more force than feels right.
• New memory runs at a slow base speed until you switch on its profile in the BIOS: XMP on Intel boards, EXPO or DOCP on AMD boards.
• Random crashes after a memory upgrade: test with one module at a time, and with the profile switched off. Mixed kits often work only at base speed.
• Windows has a memory test built in: mdsched. For a thorough test, boot MemTest86 from a USB stick and let it run overnight.

the front panel header

• The block of thin single plugs from the case: power button, reset button, two LEDs. The board prints tiny labels next to the pins, and the manual has the drawing.
• Buttons work either way round. LEDs only light one way: the coloured wire is plus, the white or black one is minus.
• To start a board without a case, or to rule out a broken power button, touch the two power switch pins with a screwdriver tip for a second. That is all the button does.

resetting the BIOS settings

• With the power cord unplugged: move the jumper labelled CLR_CMOS or JBAT for ten seconds, or take the coin cell out for a minute. Some boards have a button for it at the back.
• Do it when the PC no longer starts after a settings change, a failed overclock or new memory.
• Afterwards the settings are factory defaults. Switch the memory profile back on, check the boot order, and leave the storage mode (AHCI, RAID, VMD) the way it was: Windows does not start if that changed.
• A PC that forgets the time and the boot order whenever it is unplugged needs a new coin cell, a CR2032.
• If the drive is encrypted with BitLocker, have the recovery key ready before you reset or update the BIOS. Changed firmware settings make Windows ask for it.

thermal paste and coolers

• Clean both surfaces with isopropyl alcohol and a lint-free cloth until no old paste is left.
• One dot the size of a pea in the middle. The pressure of the cooler spreads it.
• A new cooler has a clear plastic film on its base. Take it off. It is forgotten often enough that vendors print a warning on it.
• Tighten the screws a few turns each, crosswise, so that the cooler comes down level.
• Plug the cooler's fan into the header labelled CPU_FAN. Without a fan there, many boards refuse to start.
• A rough check afterwards: 30 to 50 °C doing nothing, up to about 85 °C under full load. Above 95 °C the processor slows itself down.

airflow

• Front and bottom fans blow in, rear and top fans blow out. A fan mounted the wrong way round works against all the others.
• One or two fans more blowing in than out, with dust filters in front of them, keeps the inside cleaner.
• Cables tied out of the air path do more than an extra fan.
• A PC on the floor collects several times the dust of one on the desk, and one on carpet blocks its own bottom intake.

which way a fan blows

• Air leaves on the side where the motor is held by struts and where the label sits. The open side with the free view of the blades is the intake.
• When you clean with compressed air, hold the fan blades still with a finger. A fan spun up by the air jet runs far above its design speed, and it works as a generator back into the board.
• Go outside to do it, blow from the inside out, and do not use a household vacuum cleaner inside the case: the plastic nozzle builds up static.

the power supply

• Never use a modular cable from another power supply, even from the same brand. The plugs on the power supply side look alike and are wired differently. The result is 12 V on a 5 V line and dead drives within a second. Keep the cables in the box of the supply they came with.
• Signs of a failing power supply: restarts under load, the PC only starts on the second try, a smell, a fan that rattles.
• To test it without the PC: a power supply tester costs little and shows all voltages. The old paperclip method bridges PS_ON (pin 16 of the 24-pin plug) to a ground pin next to it. Look the pinout up before you do, since many supplies have all-black wires.
• Never open a power supply. The capacitors inside hold a dangerous charge long after it is unplugged.
• Size it by the graphics card: its vendor names a recommended wattage for the whole system. More than that buys nothing.

adding or replacing a drive

• A new empty drive does not show up in Explorer. It has to be initialised and given a volume first: diskmgmt.msc. This is the most common "my new SSD is not detected".
• On many boards an M.2 SSD switches off one or two SATA ports. If a disk vanished after you added an SSD, the manual has the table.
• Moving Windows to a new SSD: clone it with the tool of the SSD vendor or a free one, then unplug the old drive for the first start so that the PC cannot pick the wrong one.
• The standoff and the tiny screw for an M.2 SSD are in the mainboard box, often already in the board under a heat sink.
• What plugs in where: connector identifier. Whether a drive is healthy: SMART reader.

updating the BIOS without regret

• Only when it fixes something you have: a new processor that is not recognised, a security fix, a stability problem. It is not routine maintenance on a PC that works.
• Suspend BitLocker first, or Windows asks for the recovery key at the next start.
• Use a small USB stick formatted FAT32 and the update function inside the BIOS itself. Never cut the power during the update.
• Many boards have a recovery button (BIOS Flashback, Q-Flash Plus) that can rewrite a broken BIOS from a stick without a working processor. Find out whether yours has one before you need it.

Suspend-BitLocker -MountPoint C: -RebootCount 1

screws and standoffs

• The brass standoffs under the mainboard belong only where the board has a hole. One extra standoff touching the back of the board is a short circuit, and the PC does not start.
• Two threads look alike: the coarse one (6-32) holds the case panels, the power supply and 3.5-inch hard disks. The fine one (M3) holds 2.5-inch SSDs and optical drives. A coarse screw in a fine thread ruins it.
• Before the board goes in, check that none of the springy tabs of the rear port shield bent into a port.

getting into the BIOS

From a running Windows you do not need the key at all: hold Shift and choose Restart, then Troubleshoot, Advanced options, UEFI Firmware Settings. Or from an elevated prompt:

shutdown /r /fw /t 0

worth having in the drawer

• A PH2 and a PH1 screwdriver with a long shaft, and a plastic pry tool.
• A USB stick with a current Windows installer and one with a live Linux, to tell hardware faults from software faults.
• A SATA to USB adapter, to read a disk from a dead PC.
• A spare CR2032, a tube of thermal paste, isopropyl alcohol, cable ties.
• A power supply tester.
• A known good monitor cable of each kind you use.