Try resetting your PRAM, that seems to have worked for some users. In case you don't know how, restart, and before you hear the chime, press and hold down apple-option-p-r, and wait for the chime to play at least twice, though three times won't hurt it. Then let go, and the computer will start up normally (it may reset your date and time, but that's easily fixed). If not, call Apple?
jW