I wonder if your system is corrupt or if maybe you have been infected by a virus that tries to sell you a fake solution.
Are you sure you have a legal copy of W7? There are many bogus copies sold every day on eBay etc. If your sure it came from a legit source then perhaps your HD is having problems (failing) so see if the system repair disk can find any corrupt system files and repair them.
The other highly possible cause is a virus. You might try downloading and running some of the various RKILL programs and see if they find any malware. You can also use the freeware portion of malwarebytes to try and remove any infection if RKILL is able to remove it from memory. RKILL and malwarebytes are available in our
Freeware DB.