OK first disable system restore this will wipe out all of your restore points but spyware nasties etc can hide in there. Clean out all of your temporary files run disk clean up clear out all temporary internet files and temporary files. At the run prompt type %temp% this will take you to your temporary directory clean out all thats in there as well.
Now run a scan with each of the apps (make sure they are all updated) but reboot in between each scan so they have a chance to finish there cleanup. Also run a scan with your antivirus app and I would add a2 to the list as well.
If the problem still persists you will need to download hijack this and post a logfile to click here a expert will then help get you cleaned up