You will need to go through a process of elimination.
On the non working machine disconnect everything that you don't need to post the machine. So
Unplug the IDE cables from the motherboard.
Take out the graphics card if the motherboard has on board graphics but leave it in if the motherboard does not have onboard graphics.
just use one stick of ram.
disconnect the keyboard and mouse and any other device plugged in to the machine apart from the monitor cable.
take out any pci cards that are in the motherboard.
So you are booting with just one stick of ram, graphics, cpu with HS+f.