Help: My PC turns on then immidiately off!

[Its Muffins]

Hey, this is my first post of many more to come hopefullly.
I just built a spare computer using some old and new parts. I bought a new CPU for a bugdet price. I bought a used Intel LGA775 processor with no cpu fan (i will use my old one) and installed it. Then i turned on my new spare computer and everything looked okay, until the user login screen comes up. Then the computer crashes and turns off. What do you think the problem is and how can I solve it?
Any help/advice is greatly appreciated.
Thanks in advanced.

 

[chris312]

What kind of power supply did you use?

 

[Winly]

did you do a clean install of Windows? because if not you have to. and also to check if your power supply can handle the power requirements