Inspiron 600m won't boot

Help! Our Inspiron 600m won't boot at all. I know the power jack needs to be replaced because the end won't stay in place, but even with a fully charged batt. the power and batt lights come on and absolutely nothing else happens. I've tried other batts, a docking station, other power supplies with no luck. I've reseated the memory. I've opened it up and cleaned (huge glob of dust and pet hair at the fan were removed). Now what? The computer tech our office uses (an architectural office full of Dells) says "oh, must be the mother board".

Thanks for any suggestions.