Could Not Locate The Malware / Computer Randomly Shut Down

I have a problem that's probably tied to another problem. I opened an e-mail that I shouldn't have and got infected with something. I ran scans from Norton 360 and SuperAntiSpyware and other online scanning sites but I could not locate the malware. I paid a Symantec consultant to remove the infection from my system and he says it is clean. In the meantime, because my computer would randomly shut down and I was afraid that it would not recover, I reformatted my hard drive and re-installed all my programs. My computer does not recognize my video card and I have put in countless drivers to repair it with no success. Although my computer is more responsive and stable I am still plagued with random shutdowns from time to time. It sounds like you would hit the enter key and it would stick and continually click until I get a blue screen.