Dell don't lock hard drives - I think the problem is more to do with the new bootloader/manager that Vista uses (don't know too much about it, except that it's not the same as if you were reinstalling or dual booting XP)
You can't flash a BIOS onto the motherboard if it is not even completing POST - I would suggest to take what those folks say with a pinch of salt.
This is a hardware problem, so initially you want to begin by eliminating what you can to complete POST.
Minimum you will need is processor...
I think he means to power it up after you've placed the jumpers in a 'reset' configuration. This is motherboard specific I believe - not all require that to be done.
have you tested the monitor on its own to see if the self test is displayed? (testing the monitor to see if is the cause of the problem)
can we try a different video cable?
if it has multiple channels on the monitor (most dell widescreens for example), is the right input selected?
can you...