you're infected with spyware 101%
I used to catch some f****** anoying spyware, can't remember it's name...
but I had the similar symptoms..
open the task manager, and see if you're running any strange processes (you can always enter the process name in google and get a good explanation what it does, is it infectable, what is the risk of being infected, etc etc...)
if you find any strange, close them immediatly,
run antivirus, spyware scans, and also try running "Hijack this" to see if there are any suspicios things on your machine.
Also, try running this in SAFE MODE, because some spyware makes it's folders "system" (invisible), and then, some scanners will just skip them...
P.S.: Some types of scumware is very hard to remove (scan, and click on remove won't help), so be patient, and keep trying