If you are really in a hurry and short of time the quickest way to solve your problem is to rush out and buy a new machine with the OS already loaded on to it. You could be up and running within minutes of getting home. A virus security product is a good investment too.
Your question, however, is a little vague - you fail to mention the OS (you know: XP Home, Service Pack 2) or what is happening to your system (you know - this is happening when it shouldn't or perhaps - something not happening when it should).
So a new machine might be a really good option and take care what you download - there's some nasty stuff flying about.
Good Luck
Peccavi, November 2008