According to a thread on the Apple discussion forum symptoms include blank displays (including external displays) after installing MacBook Pro EFI Firmware Update 1.5 and restarting their MacBook Pros (and sometimes just putting them to sleep). According to AI:
Most common solutions fail to resolve the problem, including resetting the PRAM. A small number have successfully recovered by finding workarounds to restore firmware and deleting display sleep preferences, though some also report trying the same without success.
The problem is reported to affect mostly mid-2007 MacBook Pro systems and hasn't yet been acknowledged or addresses by Apple.