MoBo or CPU Failure?
 

After my recent problems with a virus/worm infection in my PC, I thought I had it all under control again.

However, over the past few days it has suffered random failures of the USB keyboard output. I rebooted after changing to a spare PS/2 keyboard, no change.

I also carefully cleaned off the dust from the innards, and cleaned and reseated the CPU heatsink and fan (which was running). I noticed this made little difference to the running temperature according to the BIOS's temperature monitoring facility.

This problem went away for a while after I allowed the PC to cool right down before rebooting, only to recur later at random intervals.

Today I rebooted after another failure, only to hear a POST beep code of 1-8-2-1.

Nothing on screen shown, it doesn't get as far as switching on the video output. Suspecting a video card failure (AGP) I fitted an old PCI video card instead. No change, same beep code. I disconnected all the peripherals, same beep code.

I've also reseated the DIMM modules and tried them singly in each slot.

Anyone got any further clues? The title gives away my own suspicions after all this.

Who makes the bios?

Slightly embarrassed to admit I never noted this. It's an Asrock K7S8X ATX board with an SiS chipset if that is any use.

I think it's an AMI bios. You could have a look here:

PC Hell: BIOS Error Beep Codes

Although that sequence of beeps is not described & you have extensively removed components to isolate the problem. You might try the video card, ram etc. in another box to confirm they're working?

Bios codes here

BiosCentral - AMI BIOS Beep Codes

Today it looks like the power supply has completely failed; it switched on very briefly and then died. I'll try another before doing anything else. Looks like I'm in for a complete rebuild.

I'd say it looks like you're in for a complete rebuild:p

Face it ST, if it were a horse, you'd shoot it!

I think a shooting might be too late! It's now an ex-computer, deceased :sad:

An X box? ;)

Good, but notoriously noisy...

Then again, that is a viewpoint from the media centre community for which they can act as extenders. My guess is the surround sound gamers don't hear the fan...

Overheating
 

It's Summer in the UK and it's quite humid, therefore little heat transfer to the atmosphere from humans, and heatsinks

The SITA PC at work has been playing up lately - 1 PC stand (air underneath) and moving the PC to one side (stops books being placed against hot exhaust vent) and it starts working again (100ft of paper started printing at 4am this morning!!!!)
The PC now has a marked (with marker pen) air gap beside the PC case to prevent the machine from overheating (about 1.5")

My own PC at home has the side off permanently to aid cooling, but will still occassionally shutdown during summer months

Not necessarily, a good smpsu will shut down if it detects a short/open circuit on the mbo.

unclenelli - a popular myth! In fact, if your case is halfway decent and you have a traditional fan setup, you will actually get better cooling with the side of the case on, due to improved airflow over the mobo. See it thus: If you have a CPU fan and a psu fan, with the side fo the case off, both do a reasonable job of cooling their respective parts. With the side of the case on, they also draw air over the rest of the mobo, the expansion cards, drive bays etc etc. This can be further aided with front of case/back of case fans.

Provided you have a decent case... and dont have millions of pesky IDE ribbon cables all over the place!