I have two shells that I'm looking to revive at some point. One of them is definitely worth my time and energy to rebuilding if necessary, the other not so much. I removed the hard drive from the prior one, and I believe, also from the latter. Neither will turn on. The mother board lights come on but the front power light does not. I went out and bought and multimeter to check the power supply but then I realized that the lack of a hard drive might be causing this issue. Is this common? Do I have to re-route the cables somehow after removing the drive?
Your box will normally be able to boot up without a HDD. At the least, you should get a screen after the BIOS stating "Can't find startup disk" or something to that effect.
The things that would keep the PC from booting are:
A bad electrical connection - shorting out, or incorrectly plugged in
CPU fan not being attached to the correct headers
PSU is dead
PSU cables not properly plugged in
One more - this only happened to me once - plugged in the molex and the SATA power on an HDD and it wouldn't turn on.