Hi
Sounds nasty, I've found two links that might help.
Hardware Reset - T-Mobile Pulse - DroidDog - Forums
and
G1 hard reset - Android Community Forums
Neither of those is for the pulse, and my search through the manual (I'm looking up other things anyway) hasn't brought anything to light.
Hope you get it working again, I've had mine for 2 weeks now and couldn't live without it