Magnus_4 :
basroil :
Magnus_4 :
But i do not have the disk, because i bought this computer 2nd hand.
Then you're up a creek without a paddle. microsoft's ISO downloads are only for retail licenses, so unless you can find a friend with ANY windows 7 installer disk (literally any will work, you just need to copy the disk, remove one file, and burn the new iso), you'll have to hope paid antivirus from bitdefender, kapersky, etc will help.
Sound like buying a new computer is a way easier step.
If you like paying money to people that sell computers, it's great for them LOL Don't worry about using a premium anti-virus, I've yet to see one do that much better in tests where it's worth using over a free one like AVG or Avira.
Check places like Craigslist, there are plenty of people around who have Windows 7 disks that can re-install Windows for you for a lot less than a new computer costs, just make sure you have your license key handy or you'll need to pay another $100 or so for a valid license.