Need Help, Computer wont start up

Hi everyone I need some help.

I built my old computer and everythying is fine on it and I have been using it for a year now. Recently I decided I wanted to upgrade so I bought a new case and new CPU and Motherboard. I took the videocard, sound card, ram, dvd drive, floppy drive out of my old computer.

What was left of it was the case, the power supply, the CPU, motherboard, which were all untouched. I then decided to put some stuff in it and give it to my sister. So I bought some new RAM, CD drive, hard drive, sound and video card. Installed it all and then my problem happens.

I turn the computer on and it starts up for about 3 seconds and then shuts down. I cant even restart it at this piont all I can do is unplug the cord from the back of the case and put it back in to try and turn it on again. Every time I get the same result. I have tried many things and many combinations of taking out all the extra stuff like the CD drive to try and get it to work. I even tried starting it with just the CPU attached and still the same problem. I thought maybe the motherboard I broke some how so I had it replaced through warranty and it still does the same thing. So i know its not hte motherboard. the CPU looks fine and was untouched so I dont think its that.

I have no clue at this point whats going on. I am thinking of replacing the power supply now, but I cant imagine why it would be that since the computer starts up for 3 seconds at least.

I need some major help with this I am totally lost.

Mike

[Jason425]

the psu isn't powerful enough.. think about it.. it gets most of the stuff goin but not all of it..