Maybe something like this will work for you:
http://www.amazon.com/eForCity-Batt...051916&sr=1-7&keywords=htc+inspire+4g+charger
It's a wall charger for the battery. Hopefully you can get it fully charged and then insert it into the phone. I bought one of these with two slightly larger-capacity batteries for $16, and I'm happy with it. This package includes just one regular battery, and it's around $7. Look for other battery combinations if you're interested. I don't know if this will fix your problem, but it may be worth a try. Also, have you tried starting it up in bootloader mode?
Thanks for that - I'm about to go and pick up the phone right now, I don't know what they've tried but I'll try to get the bootloader to work.
Failing that, a friend of mine gave me his old Samsung Google Edition so that's a very good substitute.