I would start by removing everything that you dont need, things like, Sound card, network card, Leave 1 stick of ram in there, unhook the HDD. etc etcgimbi said:
If it boots up then slowly start adding each part 1 by 1 untill it does not boot and that will be your problem.
Now if it does not boot then try some things like,
- Try other ram stick and remove one thats currently in there.
- Try different video card
- Try different monitor just to make sure
etc
If that still does not work, try another powersupply.
Post back with results.
Ciao