If this is happening for no apparent reason, post your problem in the SpywareBlaster forum click here.
If your PC was infected by anything recently, download & run HijackThis click here.
Post the resultant log in a dedicated HT forum click here (list in the left column).
You can also do a quick DIY HT analysis via click here. Do NOT manually remove anything on your own - ask for help on one of those forums.
All the best with it. G