gdement

Hard to say, but the first time I did a repair on my Thinkpad I accidentally broke off the lid switch, which caused the screen to stay blank. Check if your lid switch is still intact, other than that I don't know what else to suggest. It seems unlikely that there would be anything wrong with the bios, but on the laptops I've seen the CMOS battery has been in a marginally accessible location under one of the back panels. It'll probably just look like a coin-cell battery with tape wrapped around it and 2 wires hanging off.

Unplugging unnecessary components is fine, but you won't be able to reach the POST screen without memory installed. The BIOS can't get that far without it.

Try to find a service manual on Compaq's web site if you can. Those are very helpful with laptops, but not always available or easy to find.