Well, with that amount of RAM, I think the problem is not Vista but an infection. Can you please try and scan any external media from which you are transferring your data? I believe the backup source has been infiltrated and infected in some way. Please try and scan it with AVG and see if it has any infections. Our Malware experts will take the case as soon as they come online so please bear with us till then.
Also, post back the results of the scan as soon as possible. Good Luck.
-- Goku