Re: What else could it be?
honestly, i hate to do this, but the best option sounds like it might be cheaper to build a new pc. you can get a decent intel mobo/cpu setup for about $200, amd for about $150, graphics for about 50 (if not used for gaming) 150 if for gaming, ram (ddr2) for about $60 for 2gb, hdd's (if your old one is still good) for about $50 for a 160gb.
but before blowing money on a new pc, how many sticks of ram do you have for the pc? try doing a barebones boot: just one stick of ram, no hdd, no graphics card(use the onboard), no cd drive, etc...just cpu and ram.
if it still doesn't boot, try resetting the bios, if still nothing, try different sticks of ram and try using different ram slots. check all power connections to the board, make sure the cpu is installed correctly with no bent/missing pins. also make sure the heatsink is installed correctly, and the power connector for the heatsink is connected to the proper connector on the board, usually near the cpu. just try all options you can think of, and report back.
and the keyboard lights not lighting up means that its not passing post. usually a cpu, ram, or motherboard problem. just use process of elimination. get some working ram, test the cpu in another computer if possible, and a known working cpu in the computer if possible also. same with the ram.