One you could take a look at there is found in the display properties under the "customize desktop" button seen in desktop tab. Once there click and open the "web" tab to see if the active desktop is or something tried to set that active. You may be seeing a blank page.
Ad Aware is a good one along with the AVG Anti-Spyware remover found at
http://free.grisoft.com/doc/5390/lng...i-spyware-free along with the free AVG 7.5 update for the free version. If you still don't find any type of malware it may be hidden deeper. Symantec has a free online scan found at
http://security.symantec.com/sscv6/h...tjsax=1&bhcp=1