screen very dim after installation of Inverter/Airport cables

Computer ran great, excellent image - no problems in OS 9.3. Upgraded to OS 10.5.8, still no problems, but computer didn't recognize the airport card, bought another one, still nothing. Next step was to install new Inverter/Airport cables. Very difficult! Upon reboot, I can barely see the screen, nearly completely black. I have tried the brightness key, no results.