Hi everyone i got a little problem and i wasnt sure where to post but i think it could hardware related.

The problem is as follows. My desktop machine keeps reboot after left being powered up.
Some time it may have been only say 15min since boot up other times a couple of hours.
Sometimes the reboots feel random and other time when its running a scan or has a lot to handle ie firefox has a lot of taps open.

I have currently updated all drivers and applied all system updates.
To counter the problem however nothing appears to be working.
I have moved the system to allow for better air in take for cooling.
I have run malware bytes to check for infection and also run spybot search and destroy

My spec's are
windows 7 pro sp1
3gb ddr 2 ram
80gb ide hdd
640gb sata hdd
amd phenom x4 2.80 925 (95w)
asus hd6770 1gb
g7 power extreme 580w
ga-ma74gms2h
2 x cooling fans
standard dvd-rw
old 54mb wireless card
1tb desktop external hdd

Any help you could give would be greatly helpful
thanks digidude

Try a memory test using memtest86. There's the possibility that some part of the memory cannot be paged properly due to damage. It's also worth checking to see if it's an NT STOP error, because it could be more than RAM we're dealing with. Take a look in Event Viewer or disable automatic restarting and see if it is a BSOD.

But what if it restarts during memtest?

Then it's a more serious hardware issue such as the motherboard itself etc.
A memory error is highly unlikely to cause a panic in memtest anyway.

Power supply? (i think not)

Is quite unlikely the culprit. Though that said it is a cheap power supply. That's the sort the cheap ebay builders use.

after digging around no has anything positive to say about the power supply unit and thanks for the advise... the mb was only a cheap one out of pc world it was on clearance but its only been in there a year and half and the power supply got put in say 7 month ago so just before xmas.
i will run the ram test and see what happens

RAM RARELY causes a computer to simply lose power. At most it would cause a fault somewhere and cause a kernel crash (Even during POST). In my experience, it is almost always the power supply. They are the most vulnerable part of a machine these days. If that isn't it, it is the motherboard/cpu, which you should replace together anyways.

He says reset though. Memory errors can be common with cheap RAM which would not surprise me, the PSU seems cheapo.

Resets can be caused by:
- PSU overload or short circuit
- Bad drivers causing a silent BSOD
- Overheating CPU or other components
... plus more but those are the most common from my experience.

This may sound quite elementary but have you tried leaving it on safe mode to see if it still restarts? Its a broad diagnostic but it should leave a tell tale sign of hardware issues if it still restarts. I once had a faulty driver which kept freezing my comp, in safemode it didn't because it was disabled. All I had to do was reinstall a better driver for that issue.

Ok so i might have found the culprit Soulman i ran memtest86 for 6 hours 30mins and it throw a lot of error back at me. But it did not restart until i booted into windows 7.Seem like almost straight away once the deck top had loaded and firefox loaded that it restarted.
to possible over heating my current temperature stand at

speccy v1.13
Amd phenom II x4 925 53o c
motherboard 48o c
amd radeon hd 6770 41o c
80gb ide hdd 39 oc
640gb sata hdd 37o c
and i been powered up for 55min and no restarts yet "touch wood"
ive yet to try safe mode yet as i wasnt sure it would make much difference...
but i load in safe after this post and go from there... any suggest on how to check for bad drivers as device manager says there no conflicting drivers...

Try updating your drivers, that should loosen out any culprits if you believe it's a driver error (which I disagree with here). However seeing as the system has worked until now for seven months then I doubt it could be a dodgy driver. Possible but unlikely unless you update on a regular basis. Best thing to do is to read up on drivers and see if anyone is having issues with that particular driver. However at this stage I am convinced there is a memory problem. If your memory is throwing errors, it's time to replace it. Your temperatures are perfectly normal. TJMax for that CPU is 100*C I believe anyway, so it's very unlikely it's overheat protection. Plus, overheat protection turns the computer off, unless the motherboard has mental issues. Beg/steal/borrow some RAM to try in your system. If it works with the new RAM it's time to bite the bullet and buy new RAM.

problem i believe is now solved until it proves me wrong.
soulman you were right a again one dodgy stick of ram was causing the issue.
i remember when i first set out to build this little beauty started out as a bag of second hand parts from a local store the bag cost me £25.00 and included 2 sticks of 1gb drr2 ram plated akasa (one got put and the other left out as i was given a 2gb stick and there only two ram slots),a hdd 80gb ide, a cpu old p4, nvidia 8600gts and the rest i just built up got the new mother board as i said before and new cpu and a case and psu and went from there the nvidia 8600gts never powered at first due to not enough power i worked with the on board for a while till the psu give out on me and so got it replaced with the cheap 'o' one the G7 extreme... and i resided to try out a bit of gaming and got the Radeon hd 6770 and by chanced tried the old nvidia card as well and it worked so i kept it in for a while and until restart problem started but the issue still carried on even after putting back the Radeon hd 6770 in... that when i decided this has gone on long enough so desided to ask for some help...
The solution the old 1gb got removed but lucky i had its brother still that got left out of the build and switched the two... i have gone on enough now the reason i didnt bring up the drivers cause done some research when buying some of the later parts and only driver could any trouble and that was the wireless card and to add all updated drivers come direct from the proper site
digidude out feel free to lock it now mr mod thanks for listening

Glad you have it working. If you can ever afford to replace all the RAM, I recommend you use some Corsair or Crucial. They're like tanks for reliability from my experience. Akasa do decent cables and sometimes coolers but I wouldn't put RAM past them. Same can be said for Samsung. All my years old Crucial and Corsair stuff has never once went on the blink no matter how long a machine has been up. I even have 2x256MB Crucial SDRAM sticks in my PowerMac G4 (1999) from 2000 and I've never had any trouble with them.