A couple of months ago I built a new PC which apart from glitches working with Vista x64 has been a very well behaved machine. Recently I had a couple of lock ups (don't know the cause) and I also once when booting I got a coloured pattern on the screen before bios (so I reset it that time). It behaved afterwards. Most recently I left it on overnight downloading off iTunes and it locked up. After resetting it it booted up fine. Switching it on a week later it now does the following:

- Power light switches on and Ethernet LED flashes (normal)
- Fans switch on (normal)
- Fans stay on for a few seconds
- Fans reset themselves
- This loops around

The fans normally come on initially, switch off/quieten and then it boots into BIOS. However in this case it seems the system resets itself instead of getting to BIOS (or even GFX Card BIOS)

I now have set up a barebones system outside of the case to identify the culprit. This is:
- Motherboard
- CPU + Cooler
- PSU

I anticipated a number of beeps as there is no memory plugged in, however when testing this, I got the same pattern of behaviour as before. I have tried resetting CMOS using the jumper and removing the CMOS battery for a few minutes then switching on.

My gut feeling is the mobo as if it was the PSU then this problem most likely would be intermittent and from what I have read CPU's are pretty reliable under most circumstances.

Is there something straight forward and obvious I am missing and does anyone have any suggestions as to what this might be?

Thanks for any advice

Sounds like you are on the right track, At this point especially considering the age of the computer you shouuld be able to contact the manufacturer of your motherboard and get a RMA # from them and maybe an advance replacement depending on the brand where they send you the new board and you return the old one in the packaging they sent the new one in.

That's my plan, in fact if I can narrow it to the motherboard I am planning on getting a new/different one, RMA'ing the other one then possibly ebay on it. It's by J&W who supply a number to overclockers.co.uk however I would feel slightly safer with Asus/Abit Motherboard.

I have a 5/6 year old PC so I was going to see if I can get the PSU out of that one to see if I can eliminate that as the source of the problem. I hope it is that however my gut feeling is that I have to switch motherboards (not a fan of removing the CPU cooler and the CPU)

I am also thinking that it is the mobo that is the main issue, CPU should be fine and you have already tried most of the other things to round up on the mobo alone.

Raj