Go to start>run, type in msconfig, click ok.
Go to the startup tab, uncheck everything but systray. Hit OK, and reboot. If it works, great, its a background program causing the issue. You can recheck them one at a time to find out which is causing it, but its likely spyware or virus. I would start by getting spybot and ad-aware from download.com, update each, and scan. Use one at a time, empty the recovery or quarantine in each when you are done, or they will fight each other.
Matt J.
Please always take the time to backup any and all data before performing any actions suggested for ANY problem, regardless of how minor a change it might seem. Also test the backup to make sure it is intact.