Since everyone's talking about hardware problems and you say that you built your own system, I suggest getting into the system and re-seating all of your connectors. IDE ribbons/SATA cables, IDE/EIDE devices, AGP devices, etc. If you "rebuild" the system with the current components (sans the proc), you may fix the system without having to go through all this mess.
Again, just pull everything out and reinstall it all. Never know when a poorly seated DIMM or screwy AGP video card might cause a boot failure.
Reseating is a very good approach. Here in Florida there's a lot more oxidation. I've reseated components numerous times and been successful
Not a bad idea at all. Shouldn't hurt anything to do it anyway. Probably go ahead and reseat cards and memory while you've got it all apart :-)