I have a similar issue with a CECHE flashed with a progskeet. I've used this guide and the ps3 dev wiki one.
Everything goes well until it's time to flash from fsm. I can get the challenge/response from the ps3 entering fsm. No matter what usb stick I try for the flashing, the system powers off after a few seconds. The hard drive has been checked, and several usb sticks have been tried. I'm not sure what to try.
Any help is greatly appreciated.