What's wrong with my computer?

Yesterday, I reached home. I decided to sit behind my computer and go to Youtube to flame some noobs. I turned on my PC, then it asks me do I wish to open it with last working configuration or normally, I tought wtf but I choose with last working. Then it loaded few seconds and when Windows XP loading screen came, then the screen flashed blue for a sec. and then it shuts himself down (WTF!). Soo I turned it on again, but this time I choosed normally, but it does the same thing- it reaches to the Windows XP loading screen, blue screen flashes for a sec. and then it shuts down again.I have tried many times, it just doesn't work!!!!!
Any ideas what I should do to get it work?
OH, and by the way I am behind my other computer soo dont wonder how I am posting this.

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