My 15" TiG4 wont boot from either the hard drive or a CD. I get a flashing ? in a folder, alternating with a Mac smiley face. I've tried reseting the power monitor, reseting the NVRAM, reseting the PRAM, holding the 'C' key while trying to start from the original systems CD and/or the systems software restore CD. Also ran the hardware check CD and all showed as well. I'm not certain what to do beyond this point? Is there a firmware modification I can make after starting-uo and holding the option/command/O/F keys?