First try this:
Clear all your Cookies and delete your browsing history and tick the box 'Stop popup windows'. Close your browsers and shut your pc down and reboot.
Post back if you need more help.
What antivirus program and antimalware/spyware do you have on pc? Do full scans with them to check for any problems.
Download and install SpywareBlaster from one of the links on this page
it will not conflict with any of your other programs, it is free you just have to do manual updates of it's database. All you need do is each week check for updates manually. This will stop most malware/spyware from being able to invade your pc in the first place (it is not a replacement for your other antivirus anti malware/spyware progs)