OK... other than "try everything" (which I think I've done except replace the PSU), nobody has a specific idea on this... that's OK.. thanks for the try...
You should have a backup for trading anyway. Get a new comp. It is most likely a bad HD or a software conflict.
It's a Dell Vostro el-cheapo.. could probably replace it only with another OEM... likely not worth it..
Scat, Everything you describe point to a fubar MB. If you are hearing a beep on the motherboard and getting a visual color change on the monitor, you are certainly getting power to the MB. If you wanted to be more thorough, you could get a DVM and test the PSU outputs, but I'm doubting that's the problem. Blue Screens can be due to viruses, but the fact you can't even see BIOS and already swapped HDs points to MB. Did you take out BIOS battery and test the voltage? Other than that, I would yank every single peripheral (hard drive, RAM, etc) and again see if BIOS surfaces. Simple process of elimination. It ultimately points to the MB. If your PSU was completely fried, you woudn't be seeing any monitor changes. Could even be a loose monitor connection, or loose video card driver possibly. Tighten those up. The good news is, even if the MB is fried, the HD is likely ok in which case you can salvage the data by piggybacking it into a different computer. I once had a bent pin by removing the CPU with that kludgy connector spring, and had to straighten out hundreds of rows, yet the bios was still fine. Anyways, GL. I've been through or seen most problems, and aside from troubleshooting with the DVM, it sounds like MB issue. Unfortunately, if it's a dell, you'll may have problems getting away with swapping the HD onto a new motherboard and using the existing win license. That's the incentive to save it if any.
i had problems with several dell desktops, presumably power supplies. the symptom kinda like yours and there is yellow/amber light on the power button. google "amber light dell problem" or something like that if this is your case. good luck!