There are a lot of different bits of malware that can do what you describe and no matter what you'll need to perform a scan.
Do you have any anti-virus or anti-malware software? If so, try to run a scan of your entire computer. If not get one. This one's free:
You can also download free anti-adware software like adaware
and run a scan.
Please try both, and remove any threats they report and let us know how it goes.
Edit: you say you don't have internet access, but you are on the internet now. If you don't have AV and anti-malware software you will need to download it on another computer and get it onto your infected machine.