the slots and ports are:
IDE: for Hard drives and CD/DVD ROM/burners
SATA: for faster Hard Drives
DIMM: for RAM
CPU socket (in your case 754)
power cables, the biggest one into the motherboard, and sometimes there are some for frontal USB and mic + speaker ports in your case, the 4-pin Molex cables into the Hard drives and CD drives, and sometimes in your video card (in some X800's and 6800's)
and also, check that everything is pushed in correctly: one time I had a problem with this, had a black screen when I powered on, pushed in the RAM a little more and it worked