Computer problems

[.Socrates]

Right now I am typing from my public library. It seems that my computer has gone into an infinite loop.
The last time I ran it, it was fine. I did the rotuine shut down (go to start, press shut down, then press the shutdown button.) and nothing happened.
But the next time, when I tried to turn it on, it said that Windows did not shut down properly. It had six options, of only 3 I can remember:
Safe Mode (2 others but I can't remember)
Run Windows with the best configurations that worked.
Run Windows Normally.

No matter which of these I press, it always goes back to the screen.

I press Run Windows normally. The XP sign shows up like normal, but instead it goes back to the screen.
Can someone PLEASE help me?

edit- I'm on limited time people!