My computer will not boot up, I am new to this and have no clue what to do? Please any advice would help. The computer is a little over a year old, 3200+AMD Athlon Windows XP, 160GB and 512MB, about 3 weeks ago I was not even on my computer, and I just happened to notice it had shut down and restarted, it came up on the screen that ask if I wanted to start in safe mode,but it would not start in safe mode, the screen came back up again, so I picked prompt mode then it started up and worked fine for 3 days and did the same thing, it worked when i started it the same way, then the next day it just froze up, and I was not on it, so I had to press power button to shut it down, so now the screen comes up that ask to start in safe mode or last known and other options but none of these work, every one I try it just goes back to this same screen, I have tried F12 and other keys but nothing, Please any advise help,