|What makes you think, that hackers do have access to your computer?|
Anyway, download an antivirus live cd, burn it and boot your computer from this cd and check the whole system for viruses and trojans.
After that, reboot your computer, while it is disconnected from the internet.
Back in Windows, click Start / Run and type in msconfig, then click OK.
Click the Startup tab and check the list for suspicious entries.
If found some, unmark them.
When done, click OK and reboot your computer again.
If your computer is running smoothly without connection to the internet, then connect your computer back to the internet and reboot.
When done, first of all, update your antivirus software and do a whole system scan from within windows.