My Cpu Fan won't start, I've gotten the PC to work since I last posted, by swapping out the motherboard, it only loaded up once. I figured I'd shut it down and restart it to see if it was just a fluke, but it didn't turn back on. When I turn the power switch on, and not the power button, my USB Optical mouse lights up, even though the system isn't on. And after I had shut it down last time the optical mouse stayed on. Only when I turn the power switch off, does the USB mouse turn off as well, other than that it's emitting red light. But as soon as I turn the switch on, and not hit the power button it's on. Like it's somehow just taking power from the PSU for the mouse without me turning the system on. The computer itself will probably not boot up unless the CPU fan will spin, and it was the first time I got it to work, but never again after that. I've looked for help with this question on other threads but, there's nothing like this problem anywhere. My system is.. Intel Celeron Processor 2.60 GHz 1 Gb of DDR Ram ( Two 512mb sticks ) 2 Hard drives ( One 40gb and One 80 Gb ) 1 CDW drive, 48x write speed. Intel Extreme graphics AGP Power supply that came with it doesn't work and makes a funny clicking sound where the cable that you plug into the outlet is, where you connect it to the actual power source. I've tried using a new power supply and it didn't work, the HDs will sound like they boot up, but nothing registers on my monitor, and the CPU fan does not spin at all. Basically, I got it to work ONCE, turned it off, changed nothing and it wouldn't start up again, and the CPU fan will not spin.

Did you test the motherboard before putting it in the case? Motherboards grounding out on case is the first thing to check.

I did not test the motherboard. How would I go about doing that, sorry if I'm posting common knowledge, I'm relatively new to fixing computers myself.

To benchtest the motherboard you take it out of the case. connect the powersupply. instal the CPU with HSF, 1 stick of ram, graphics card (unless onboard),Monitor & keyboard. Turn on power and using a screwdriver carefully bridge the power-on pins for a brief time. If everything is working you should get a POST beep and boot into bios. If you get nothing then remove the graphics card and try again to power on. If no beeps replace the graphics card and remove the ram. Be careful to disconnect power before each change/test. Report back with outcome/progress I used to have a signature but it disappeared and I just couldn't be bothered writing another so please feel free to ingore this.

I did so, and nothing happened, the power supply still feeds power directly to the other objects, Like the optical mouse ( which I didn't have plugged in when I bench tested it. ) and not I'm guessing the Heat sink fan Or something..

If you get no beeps with only the motherboard and CPU then one or both of those is faulty. The only way to test the CPU is to put it in a known good compatible motherboard and see if it works. As power seems to be getting to peripheral devices at times when it shouldn't, I suspect your motherboard is shot. Whether the CPU has survived the meltdown is yet to be determined. I used to have a signature but it disappeared and I just couldn't be bothered writing another so please feel free to ingore this.

Thanks for the clarification, I'll look into the cpu/motherboard ordeal. If Iam to replace both, or one of the two, will I lose information on my hard drive(s)?