I have one assembled PC with 80 GB Seagate SATA HDD along with ASUS motherboard. I assembled the PC arround 4 years back. The PC was working fine. Suddenly, i found my OS (Windows XP Pro SP2) corrupted. I started repairing the OS, but unfortunately it failed due to C drive not accessing. When i tried to fresh installation of OS, i saw the booting partition i.e. drive C is showing "Unrecognize Partition". I deleted the partition and created again and after that Windows XP was able to install. After a couple of month, the same problem occured and i followed the same procedure as before. Again after some months, the same problem appeared. I then replace the 80 GB HDD with a new 160 GB Seagate SATA HDD and installed the OS. Amazingly, some months later, i found the same problem with the new hard disk. I again follow the previous procedure. This thing again happened after some months (max. 2 to 3 months). I also tried with a 250 GB Seagate SATA HDD, but within a couple of months that situation happened. My OS is well protected against viruses or, any threats. So, there is no possibility of virus infection (i checked with Norton Internet Security, McAfee Total Protection, Kaspersky Pure, Spyware Doctor, ect.).
My question is what is the reason behind the disaster? The PC is backed up by APC ups. As three HDD cannot be damaged Simultaneously. Is there any possiblity of malfunctioning of SMPS or, motherboard or, something else that i cannot imagine?
Looks like a psu or memory stick failure. try memtest86+ then if after a few cycles it doesn't show any ram failure, then it should be the psu that is doomed.
Btw 10/20/40/80GB HDD were flawed and the 160GB COULD be the issue as well. That happens with old tech so you might have to get a better HDD in the future.
EDIT: Also look carefully at all your cables. If any cable is damaged it can corrupt data. IDE cables tend to be damaged easily on the edges, and SATA cables tend to break, near the connectors if they're twisted for a long time. NEVER untwist a twisted SATA cable, leave it as it is until it's no good anymore.