When did it start? A week ago? Two weeks ago? Do a search for any .exe's, .dll's, .tmp's and .~ (null) files that are timestamped from the period. I wrote a tutorial on manually removing rogue apps, might take a look at it (if you read it though, don't rush to start deleting files willy-nilly).

Did you install and run Ccleaner as suggested by nihil?

May I also suggest another web browser on your computer? Opera and/or Firefox should work fine and you'll have something that doesn't drive you crazy in the meantime.

That HJT log is as thin as I've ever seen one. Is your HJT log generated from safe mode? If it is, try posting an HJT log from a normal startup.