Recently my has had trouble booting up. When I turn on the system, it turns off, then back on, and off, then finally, back on but the lights are flashing red and green. Some people said that it could be due to a lose wire on the LPC. So I opened the xbox (i discovered the torx screws for the HD and DC drive were missing) and i checked the chip and wires. The wires seemed to be in place and none were touching. I put the system back together and tested it. It worked, and I thought I was in the clear. Then the next day, the system wasn't booting again.

Does anyone know what's causing this problem? Could the missing screws be at fault? TIA.

Its not the missing screws. They don't ground anywhere. You have a bad connection or a short. Do what you did the last time and make sure all the solder points are good.

I have to agree with Slomar.

The symptoms you have described are that of a properly grounded d0 trying to boot the LPC points and not succeeding. So I would check over the LPC points again and make sure they aren't touching the bottom of the case or the mod chip isn't grounding on the shielding.