My computer will not run any exe files Please help!

Hello,

Since "vista defender" popped up on my machine I can not get rid of it and I am unable to access anything from my desktop. I can not even go in safe mode and run a diagnostics. Microsoft told me that I have a sys 32 file corrupt and for $200 they would fix it. I do not have that kind of money. I am fairly savvy when it comes to computers as I used to work at a tech in my office. I did purchase a re in stall win 7 disk to try to over install on my vista but it doesn't recognize my cd either. it doesn't recognize me as admin and I have never put an admin pswd on my machine.

Can anyone please give me some advice on how to get around this issue.