Computer not working with new power supply

What are the rest of the specs of your system? Why did you replace your old power supply, broken or needed to upgrade? Does it still boot with your old power supply? Did you remember to plug in the 4 or 8 pin CPU power connector?

Gigabyte MA785GM-US2H
AMD Athlon II X2 240
Wintec AMPO 4096MB PC5400 DDR2 667MHz (2x2048)
WD Caviar Green 1TB 32MB/SATA-3G

The old power supply was starting to die, the fan would stop and it kept making these annoying noises like it was struggling to stay on. Also, I'm not sure, but I don't think I hear any activity from the hard drive when I turn the computer on.

I tried both the 4-pin and the 8-pin connectors.

Try boot without RAM, do you hear any beeps sound?
Do you have UPS attached with your PC?

3 Points troubleshooting:

1. Boot without the RAM, video card, HDD or optical drive just the CPU, motherboard and the PSU, you should hear beeps sound (make sure you have a speaker).
2. If you got that one insert the RAM, insert just one stick of RAM, boot it up - you should hear another beep. Continue with the rest of the sticks of RAM (if any). If one of the sticks didn't give the beeps then try cleaning it.
3. If the RAM pass the test, insert the video card and connect it to the monitor. You should see something in your monitor. If not try cleaning the video card or get another card just for test. If everything works, plug in the rest of the components.

Hope that works.

I just tried putting my old psu back in and the same thing is happening. Also, I tried booting without the RAM, video card, or hard drive and didn't hear any beeps. So is my motherboard fried? How do I tell what has been affected?

Try reset CMOS battery and make sure all cables are properly connected...

Just tried, didn't work.

I'm not sure if this means anything but, none of the lights on the keyboard will light up, the light on the bottom of the optical mouse doesn't light up, I have two DVD drives and only one of them is able to open. Are these signs that it's probably the motherboard? I'd be much happier if I just had to buy a new motherboard opposed to a whole new computer.

Also, I was able to test both my video card and hard drive on another computer. They both worked fine. Unfortunately I don't have another computer compatible to test the RAM or the CPU.

sounds like the motherboard got zapped just to humor the thorough disconnect all of the PSU connections find the ground and and power of the 20+4\24 and test for impedance on all the pins with a volt meter and see if any are showing no resistance and try the same with the CPU 4\8 pin power connector and see if there are any results

you dont HAVE to do those steps but it might help diagnose if your board is indeed fried

Ok, so I've basically bought an entire new computer (everything except the GPU and HDD). I just set everything up in the new tower and again the computer won't boot. I was able to narrow it down and figure out what the issue is though. It's the EATX12V. When I don't plug anything into it, the computer will power on. I tried both the 4-pin and the 8-pin connectors, when either of them are plugged in, the computer will not power on. What do I do?