I have been working on this particular computer for the past two weekends. This computer came with Windows XP Home Edition Service Pack 2 on it and it was manufactured in July of 2005. The owner recently upgraded the original 512 MB of system memory to 2 GB at my suggestion (I installed the memory for her after she purchased the upgrade) and it was shortly thereafter that I discovered that her computer had more wrong with it. The system suffered from BSODs, random restarts, and browser crashes. When I had her boot the computer into Safe Mode, it identified the OS as "Windows (Default)" which told me that the OS had been altered. It also turns out that the original Samsung Spinpoint 40 GB hard drive that originally came with this computer had died due to a multitude of bad sectors and was replaced nearly three years ago with a 160 GB ExcelStor Jupiter ATA-133 hard drive. In addition, this computer had contracted some sort of virus on this hard drive and the owner had some seemingly knowledgeable idiot remove the virus manually by editing the registry (which I believe led to the OS being recognized as "Windows (Default)" by Safe Mode).
At any rate, I have attempted numerous full low-level formats and clean reinstalls and I seem to run into various random errors and restarts. Not to overlook the obvious, I have tested the new memory sticks repeatedly with memTest86+ and the memory flags no errors. CrystalDiskInfo properly identifies the drive and tells me it's in good health, but I am unable to verify this as ExcelStor's HDD Diagnostics utility has to operate in MS-DOS mode, not a DOS window, and offers no real way to determine the actual health of the drive as it has no diagnostic tests to select in the DOS environment that the HDD diagnostic provides. I am thinking that the hard drive has a few bad sectors that are actually just starting to go bad or it does not have enough bad sectors to actually fail the S.M.A.R.T. diagnostics in CrystalDiskInfo. Also, the BSODs have all been different STOP errors with different messages. Any thoughts?