Contrary to that last answer, you do not need anything to format the hard drive. It is a simple format command. However, I suspect that is not what you mean. (Formating clears EVERYTHING off the hard drive and so you need to have the code to replace the stuff that was there, other otherwise your PC will be toast.)
I reckon you mean you want to reinstall Windows (which can include format as part of the operation). In ortder to dso that youir PC needs a recovbery partition on the hard disk or a recoveryu CD. If you do not hjave thjso you can't do it.
Having said that you seem to think that you have a virus. (Evidence??) In which case go to http://free.avg.com/ Download the free version of AVG and run it.
If your problem is actually performance related then read the many threads here on how to improve the performance of your PC.
T, March 2009