What's wrong with my computer?

Hey people, I'm on the lookout for any possible answers to my problem. I have a windows vista(don't comment on how macs are better, I know) and for some reason it won't turn on. I can turn on the tower and the monitor, the lights show up, and it gives me the option of going to safe mode(which I've done) but after that it's just a black screen with the cursor. Can anyone help me?