vista problm

My computer shuts down Windows Explorer then immidiatly turns it back on then shuts it down again and the cycle continues. It does this in safe mode as well. If I am fast enough, I can run programs, such as Windows media player, or if an icon is on the desk top, I can run a program, but I can’t turn one on by going to the “all programs button.”

I have run the norton scan, but it came up with nothing. I have seen the thread which tell me to edit the registry, but I can’t open the run even to get to regedit.