Sounds like le mobo mort! One last shot in the dark is removing the floppy drive connections (just disconnect the cable from the motherboard and the power from the drive itself - I have had problems with FDD connectors (not being keyed or having inappropriate cheapo interfaces without a housing) being on the wrong way around and having the motherboard not fully power up to save itself from some damage. This really is a stab in the dark as you haven't mentioned having the machine apart before this problem occurred.
You may have to bite the bullet and get a new motherboard - but that can be tricky and expensive depending. If your motherboard is well old (being 6months+ lol ), you may have problems locating a similar one. It sounds as though you have your data in-tact on your hard drive, which is good. You may want to consider getting that disk backed up quick-sharp, or at least stop sticking it in what appears to be a sick PC.
If you can find a similar/same motherboard then you are on to a winner, as it will be a simple replacement no new memory or cpu etc., or even no re-install also there will be a good chance that Windows will not spit the dummy and claim your copy of Windows is not valid! (can't change too much hardware before it starts winging). A huge problem with switching in a similar yet not the same model motherboard is that the installed Windows may not be able to figure out what to do with your hard disk or other important chipset driver bits.
If you know the model number / make of your motherboard. cpu type and memory type, maybe someone here can suggest where to get one, or your best alternative.
Hopefully some other bright spark will interject with a more sensible option than an outright motherboard replacement.
Sorry can't be of more help. If you were a bit closer I would come and have a look
Cheers and Good Luck!