So, you are saying that when you follow the steps to put the phone into bootloader, (hold volume down and hold power, after removing and reinserting battery), the phone does not respond at all?
I do not, have never had a Diamond, but the Touch Pro, which is VERY close. Does the Diamond have a reset button? (it should, as I have not seen a WM phone which did not.) If it does, try holding volume down, power and then press reset while holding these buttons.