computer running like crap, error messages

Ok, my computer recently started acting wacky, it wont open programs, it running like molasses and i keep getting erro messages, such as vsmon not working, firefox exe doesnt exist, the instruction set memory could not be read, and some other ones, i thought it was the memory, so i took out every stick and put them in one at a time, same difference, i was thinking maybe the hard drive, but that seems ok. I had my bfg 9600gt go bad on me, so i replaced that with a asus 9600gt, i uninstalled the drivers and put in the latest nvidia drivers 175.16, and other that that, the only changes were a bioshock demo i added.

Some users also report problems with the SecuROM that Bioshock(and its demo install).

Unless you mean a benching demo.