HD only powers up if IDE cable is not connected?

hp a300n hd doesn't spinup unless ide cable is not connected. Also, bios doesn't boot and monitor doesn't show any thing. I assume the bios is not working and so the computer appears "dead". It seems to me the bios battery could be dead and the bios has "lost" the boot program, or the MB is dead, or the CPU, or the HD controller is dead, but then the monitor would come on? It also it could be a number of things.

I'm posting this to see if someone has had this problem before I start tearing the computer apart! I am not new at this, so please limit answers that I already know, like the HD does power up with just the power supply connected, Thanks

you already mentioned that you're hard drive doesn't spin unless ide cable is not connected.
but
does you're monitor show any thing when you unplug the ide cable from the drive ?
if yes
the there is no problem, in the bios ,cpu, heat
you should only assume that you're IDE cable it self may have a short or you're hard drive it self may have a short circuits