my dell computer won't even boot. help

[Troubledyouth]

I got a dell demension 4550 a couple of years ago (3 i think). here recently the computer will not even boot up. when i push the power button all the fans and everything will come on but will shut off after a couple of seconds. very rareley can i get the computer to come up completely. i also notice when i turn the computer on that it just does not seem to have enough power when i turn it on. i have tried many things to fix this problem but none of them seem to fix it. if any one else has any suggestions to help fix the problem please fell free to post. here is what i have done to try and fix the problem

-change the powersupply to my ocz powerstream 600W (still did the problem)

-changed 2 different video cards in(all worked and still problem)

 

[turtile]

Pull the memory out and see if the motherboard makes the memory problem beeps. If it doesn't, the motherboard is bad.

 

[Bruce]

I just had a 4300 die, after it ruined 4 sticks of memory I decided to pronounce it dead.