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I've been assembling my own PCs for more than 15 years but this is the strangest error I have encountered yet.

One day I switched on my PC just to find the registry was corrupted and Windows XP was unable to boot. A repair installation from the (original) Windows XP SP3 disk did the trick and the computer was running smoothly for maybe 2 days. Then the registry got corrupted again, this time even a repair installation did not fix it, windows always froze with a black screen even before the F8 boot menu.

I got suspicious and ran memtest86 on the machine which reported lots of errors (quite strange since I just replaced the memory 3 months ago because it was obviously broken, sudden reboots, BSODs , memtest failing and the like). Although the modules are more on the high-end side of things (DDR2 1066+, Corsair Dominator 8500C5DF) I did not overclock the CPU or memory. The memory modules are on the official compatibility list for my mainboard (Gigabyte P45 UD3R).

I removed the memory modules and put in a single new DDR2-800 module, did a clean install of Windows XP and things went well again for a day or two. After some reboot, the registry was corrupted AGAIN. Since I had already replaced the memory, I suspected the HD to be the culprit and replaced it with a new OCZ Vertex 64GB SSD (with a new SATA cable) and did a re-install again. To make a long story short, the same thing STILL happened (sometimes I would only get a chdsk run with lots of FS errors when booting up). So I bought a new mainboard (Gigabyte P43-ES3G) and reinstalled windows again ... but still this did not fix the random filesystem corruption after a reboot ! I can run Prime95 / memtest for hours, the machine never gets hot / unstable , even when playing games for hours but I still get the occasional filesystem/registry corruption after a reboot. The machine is dual-booting Linux as well (is on the same disk as windows) and I never see any FS corruption there. The only parts I have not replaced yet are my graphics card (don't have a spare one lying around), my PSU and the SATA raid controller (which the boot harddisk is not connected to).... what am I missing ?

My current setup:

Gigabyte P43-ES3G 
Intel Core2 Quad Q6600 + Noctua 12P cooler 
Lian Li Big Tower with 3x 120mm fans 
4GB stock DDR2-800 (Corsair) 
ATI Radeon 4870 /512MB  
3x SATA HD attached to Adaptec SATA HW RAID
64GB OCZ Vertex SSD (attached to onboard SATA), boot disk 
1x SATA HD (attached to onboard SATA), the HD I replaced with the SSD)
550W power supply ( either Thermaltake or Energmax, would
need to remove the PSU to check)
share|improve this question
do you have check you computer for malware? – fluxtendu Feb 19 '10 at 7:46
malware doesn't cause memtest errors. – quack quixote Feb 19 '10 at 7:49
oups missed this part – fluxtendu Feb 19 '10 at 7:51

If it's not the memory, not the hard drive, and not the OS itself, your culprit is either the motherboard or the power supply. If you have the spare parts, swap in another PSU and re-test with Memtest and/or Prime95.

It may be worth verifying (with another PSU/motherboard) that the memory truly is good. If the RAM passes Memtest on another mainboard, it's a good sign your RAM is good and the problem is elsewhere.

Failing PSUs can cause all kinds of strange error behavior, so I'd start there. Of course, if the PSU is bad, it could have already damaged other components.

share|improve this answer
+1 for comment about a faulty PSU doing weird things to the computer. I had a similar problem with Windows randomly restarting, freezing during boot up, and constantly wanting to do a chkdsk on boot. Turned out to be a faulty PSU. – Kez Feb 20 '10 at 12:23

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