Will not charge or turn on using USB cable.

Two things.

HTC phones will not charge from the USB port unless you have ActiveSync on an XP or Mobile Device Manager on a Vista PC loaded.

Second, if the phone has been stored for a very long time, 1 year if initially charged, 1/2 year if not, the the battery self discharges to a point the USB port PC Sync software doesn't know the phone is connected. You must jump start a charge on the battery by either and HTC AC charger, a generic AC/USB charger will not work, or you can apply a +5 VDC voltage to the power terminal, marked + and - on the battery case, on the two outside terminals I believe. This 5VDC must be current limited for safety. The Red and Black lead inside a standard USB cable will supply current limited +5 volts at 100MA. Chop off a standard USB cable, their cheap and break out expose the Red and Black leads. While connected to the PC USB port, hold the Red lead to the + battery terminal and the Black to the (-), or other outside terminal, of about 30 seconds to a minute.

Now when you plug the phone to the PC with a good USB, the Amber light on the phone to indicate Charging, may not come on for a while, 5 minutes or so, but it will eventually. If it does not, jump the battery again for a longer period of time.

An AC charger for the 3125 are fairly inexpensive. $7 or so, on ebay with shipping. This may be the way to go. Consider getting one with a new battery. They are sold this way sometimes and sometimes for little more that the charger alone.