Windows can't boot!

My computer totally won't start up. I recently got rid of a bunch of viruses, spyware, etc... Now when I log on, my desktop background shows up, but nothing else. I can't start anything, including the task manager. When I try to log on to safe mode, it lets me click on my account, but then it says: ntos.exe has encountered a problem and needs to close. I don't have the windows installation disk because the version was quite old and now Microsoft says it's not valid. I tried to use Norton Recovery Tool, but all it showed was a vista-like loading screen, and then freezes. I have service pack 1, i had Malaware Bytes, a-squared, Spybot, and avast installed. I tried to use the Bitdefender and Kapersky boot CD, but the Bitdefender said it couldn't open the file system, and the Kapersky when gave me a blank screen. Any tips, or is my computer ruined?