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)