I'm not sure about mid-2009 MacBook Pros but I have an early '08 15" MBP which has suffered pretty much the same problem. The first issue about 6 months ago was after an install of Lion, and the whole computer went totally unresponsive. I took it to a repair shop and they told me that the OS had corrupted my laptop, through a damaged file or something else.
Yesterday, I went to wake my MBP from sleep and the screen didn't turn itself back on. I attempted to put it back into sleep but the light in the push button latch didn't fade and the computer didn't sleep. I forced a shutdown and restarted but no luck. Since then I have forced shutdown six times and removed the battery twice in the hope it'll give it a kick up the backside and get it to start again, but nothing has prevailed. The odd thing is I can use the volume keys and the caps lock and num lock lights illuminate, and I can hear the sound of the volume but everything else is dead.
I have restarted in safe mode several times but STILL nothing. In the past when my laptop has woken from sleep I have needed to put it back to sleep to get a display but the display has lit up in these cases, just not supplied me with a log in screen.
I would really like a solution to this problem that doesn't cost money and ideally doesn't take too much time; I have very important exams in three weeks' time, and all my study notes are on my laptop. I'm especially annoyed this time because I've only just got a new charger after a week of not being able to use my laptop, and yesterday I was only able to use it for a couple hours before this problem arose.
I have not installed any updates for weeks but I bought some new music yesterday, and of course I used the new charger - that's all that has been different.
Really need some help with this one.