I can understand tis situation drives you crazy. Unfortunately i'm not an expert, but willing to give it a shot so you can proceed again with the laptop.
Wild guesses: are you able and if yes did you try to connect an external screen to your laptop in order to see if it is the laptop screen or not what is not functioning.
The way you describe your problem suggests me it's not a "sleepmode" issue. Does your laptop has a seperate videocard or is it running on the motherboard with shared memory?
If it has a seperate card, are you sure this card is working fine and receives enough power (attached firm into it's socket) If you use the motherboard are you sure your memory is in order (try a MEMtest)
Are you sure the power adapter works 100% and / or the battery is still functioning.
Have you tried to work o the laptop screen with another resolution (lower) in order to see if the videodriver is stable enough to display your settings.
If i come up with more useless guesses ill post them, in the mean time i hope for you you can solve this issue. Good luck.