I appreciate your point Elizabeth, but I have dealt with this problem on a number of occasions and those programs which are started at the beginning are always the best place to start.
Taking a lucky dip of one of the huge number of solutions that might have worked for others is silly.
I have today, for example, returned a computer to a grateful friend who was having this very problem, among others. He also claimed he had not installed anything new, but new things had been installed without his knowledge. In his case, I'm pretty sure something came in with what he believed was an update to another program.
And he was using Vista!