This sounds like a virus that folows you from install to install, I would suggest the folowing
1) save all the data to an external source
2) do a secure wipe of the full hard drive in the system
http://www.stanford.edu/group/security/securecomputing/data_destruction_Dban.htmlyou can download the .iso file and burn it to a cd with your favorite cd
burning software
3) re-install the operating system (again, sorry)
4) at this point do not copy anything over from your backup, first verify that the system is stable and doesnt delete dll files and blue-screening, if this is true, continue on, if not, either it is a *very* reselliant virus (possible, not likely though) or you have a hardware issue (i would start with trying a different hard drive, and moving on from there)
however if the system does seem stable, slowly move your old backed up data to your reinstalled operating system, only doing small chunks at a time and making sure it doesnt crash. if at some point it starts showing the symptoms again, it is likely that section of data that was most recently copied that is either corrupted or has a virus.
if all the data copies over and you maintain a stable system, then problem solved!
If you have any questions, please let me know.
Thanks,
Mike