PC won't turn on?

[BloodyWaters]

I bought an old PC from a garage sale a few days ago just for fun. It is a Dell Optiplex 210L with a Pentium 4. I brought it home, turned it on, and it took me to the bios (there was no hard drive). I then disassembled it, cleaned everything, and put it back together. When I pressed the on button, absolutely nothing happened. I then unplugged all the unnecessary components, and tried again. Nothing. I thought something may be shorting out, so  I took out the guts of the system and reassembled it on a large sheet of wood. Still nothing. The motherboard power light is on, which means it's not the power supply (I've tried 3 power supplies so far). I noticed some pins had been bent on the front IO connector, so I straightened those as best as I could, but nothing. I looked for some pins to short out because the power switch might be faulty, but everything on the front panel (including USB ports, audio,  activity lights and power button) seems to connect to the Mobo in one ribbon cable. What should I do? It was working fine before I took it apart. 

 

Thanks in advance,

BloodyWaters

 

Edit: I took out the Mobo battery, wrote this, and put it back in and it still doesn't work. 

[Guest]

Is the on button damaged at all? Did you damage anything on the board while cleaning? Those are the only things I can imagine being the problem. If any components connected to the motherboard failed, it would at least boot and complain that said failed component wasn't installed.

[BloodyWaters]

6 minutes ago, LeinadTM said:

Is the on button damaged at all? Did you damage anything on the board while cleaning? Those are the only things I can imagine being the problem. If any components connected to the motherboard failed, it would at least boot and complain that said failed component wasn't installed.

I don't think the on button is damaged, just the front panel connectors. 

[BloodyWaters]

Never mind! I fixed it. It didn't have anything to do with the front panel connectors, just these two pins were shorting out. Thanks for the help!