just do the basic.. boot to safemode
then click on start->Run
then type in msconfig and hit Enter (Return) key
You will see the System Configuration Utitlity window
click on the startup tab, Uncheck all the items other than Antivirus and firewall. then click apply and Ok. It might ask you to restart your computer, you may click ok.
Then open your browser, it could be either IE , Firefox, opera... clear the cookies and any plugin installed which is not the standard stuff.
This should solve lot of issue, later try downloading spybot, ad-aware, ccleaner and do some cleanup.