I sent an email after I found out about the forum on this site.
Here's my problem.

My eMachines computer of about 4 years, never turned back on during my finals week, which was about 4 weeks AGO. At first, I opened up the computer and cleaned out the dust on the CPU cooling FAN area and the rest of the motherboard. I turned the computer back on and it was good till I accidently unplugged the power plug on power supply. Now, it will never turn on again. The power supply still works and powers..but nothing boots up to the other devices such as the monitor and the keyboard and everything else! The motherboard lights up and the CPU appears to be running. So I decide to go back home and replace it with a new motherboard and a new Processor chip and more MEMORY. I want a brand new computer, except keep my hard drives. I set up everything with the new parts and connect with with my Hard Drives. Guess what? That doesn't work either. Nothing boots up or communicates as a normal functioning computer. Same problem with new and old hardware. Hmm? Do I have the computer curse? I need a functioning computer by this weekend because I go back to school! Please help. I researched online and talked to computer techinicians at Circuit City...I don't want to bring an actual broken computer for repairs? I don't know anymore what to do. Tired of wasting and spending money. I hate computers. But I'm better at knowing about them compared anyone else I know that doesn't have a computer education.


Now. Here's the short run.

Hmm, same problem with old and new hardware?
Hmm, no one can straight up answer my problem after my research?
The computer power starts. Just doesn't boot up as a full computer. The monitor and keyboard receives nothing from an operating system that can't appear because the hardware won't tell me what's wrong!
Hmm, no beep codes..which is related to every common problem of computer boot up. But not mine because no one can figure it out.
The problem is not the power supply. I will GET an updated one with my new motherboard and CPU in a new computer case. But the problem is, why won't it start up? It wouldn't start up in my old eMachines model with the old motherboard and stuff. I'd like to know about this mystery because I rebuild my computer. MAKING sure it is a real computer instead of just show and tell.

Here's the stats.

The ATX power supply is at 250 Watts.
The new motherboard I bought is an RS400-A.
The new processor is Intel Pentium 4 Processor 630 at the speed of 3 Gigahertz.
The old processor is AMD Athlon Processor XP 2000+.
The old motherboard, I have no clue and I don't think it matters.

Is it the power supply? It failed to boot up on the old motherboard. And it sure won't boot up on the new motherboard since the new one kinda needs at least 400 Watt power supply instead of 250 watts. But it still looks really bad.
It's kind of a rambling story, but it wasn't working, so you replaced everything, but the drives, and it still doesn't work. You know the power supply is good because some lights come on, but....

I would try a known good power supply in that machine BUT all the components must be connected correctly, and function properly, and this may or may not be the case. Since it sounds like you are in over your head already, I would say call a geeky friend over to have a look or better take it to a repair shop.

Sometimes you just need another pair of eyes.Just because some lights come on doesn't mean the power supply is good. Need to test with a different one. Might the new motherboard require an additional power plug that your power supply doesn't have? What's the wattage of the power supply? What kind of new board / processor did you install?

Are you absolutely sure everything's hooked up right?