I too missed your post.
Did you get it fixed?
If not then did you try unplugging everything from M-board & PSU.
CD/DVD's, HDD, Floppy, everything-USB, printers, speakers
* Leave the ram & CPU as is *
Then pull ALL cards from M-board.
Buy an old $5 PCI vid card (or borrow one) & plug it in (no AGP cards!)
All that is connected to M-board now is PCI Vid card & monitor, keyboard, PSU
If it still doesn't boot, but gives different beeps, try (turn off pc first) plugging mouse in.
Do you still get the 1 beep & freeze?
If you do, then borrow a friends PSU, or buy one.
Unplug the old one from M-board.
Plug in new PSU
If the board now works (no beep, just asks for OS) then your old PSU is dead.

If it still beeps with friends PSU, then it is hardware (cause your HDD isn't connected ergo no software)
But then it can only be RAM, CPU, M-board...