Bought a Canon G7 off the bay for 15 quid, "untested" - worth a punt at that.
It arrived, I bunged a battery in, dead as a dead thing.
Bit of research online, found there is a generic fault (system design flaw) whereby a screw comes loose just under the top RHS - it usually shorts out the power board, either killing the board completely or blowing a sub miniature surface mount fuse.
This was the latter, and I bridged the fuse with some 1 amp fuse wire (the actual value of the fuse), some excruciatingly fine soldering there !
It works. Happy me, a 90 quid camera in my kit.