My computer losses power during start up. How to solve it?

I am using a pentium 4 pc with 3.0 Ghz Hyper Threading processor 1mb cache, Intel GBF 865 Motherboard, 1 GB Ram and using the Bulit in Video Adapter of my motherboard, i.e. Intel Extreme Graphics with built in 64 mb memory and it uses a buffer memory of 16 mb from my ram. I am using Windows Xp Pro SP3. Whenever i start my PC mostly it gives me 4 beeps and a error message stating that my computer was previously shut down cause of thermal over heating (even though i had shut down my computer properly and there were no over heating problems.) i press f4 key to continue with the start up but halfway through or sometimes after the windows is loaded completely my computer losses power. it just shuts down itself. i then startup up again and same things keeps happening 4 to 10 times then eventually in some luck try it does start up and stays put and works completely fine. but when i shutdown and start again same thing happens... Please help me. And i'm pretty sure that its not a processor over heating problem. i even disabled the hyper threading but no change.... Please tell me if its my power supply or my mother board?My computer losses power during start up. How to solve it?
My guess is the power supply. I used to have a similar problem, and it turned out that my power supply had lost wattage over time and so it was difficult to supply enough power to all the components during startup. Once i got a new PSU everything was fine again. I recommend getting it checked at a local PC-shop.My computer losses power during start up. How to solve it?
try switching the power supply and if that doesn't work put some dielectric grease (thermal paste) on the cpu, b/c it might also be a over heating issueMy computer losses power during start up. How to solve it?
i'd start with the power supply and then if that checkcs out ok then suspect other things, it could be a short it could be in the power supply or the motherboard i'm' guessing also, but honestly you should more than likely take it to a pc repair shop to acheive your true answer