Can't reset laptop to factory settings

I have a Gateway Z06 laptop with Windows 7. It got some sort of virus that I couldn't remove no matter what I did. I had no other option but to reset the laptop, but when I started the Windows Boot Manager I got messages saying the following programs were corrupted:

winload.exe 0xc0000428
memtest.exe 0xc000000f

I've seen comments saying that I need to insert the Windows 7 CD, but my laptop came with the OS already installed. What can I do?