Just curious, when you're plugged into the computer, does Internal Storage show up at all in your drive list? If you can see that, then maybe you could try to force a flash to stock from storage.
Here's that info from one of the threads here:
http://forum.ppcgeeks.com/showthread...red+bootloader
If the drive doesn't show up, then likely what someone else said is the case--a bad usb/charging port on the phone. In your initial post, you mentioned two Diamonds... is it doing the same thing on both?