Macbook Pro wont wake up from sleep

I have a late 2008 version mbp 15 inch. 2.4ghz 4 gig ram 200 gig hd. Whenever it goes to sleep because the battery runs to low, I plug it in and it won't wake up from sleep. The indicator light on the latch button stays at full brightness, but no moniter. I have to end up pushing the startup button till it shuts down, and restarting. Any idea's?

Mine does this from time to time in Windows. Usually you can adjust the brightness of your screen and it will wake up. Press F1 and F2 to lower and raise the brightness

Thanks for the reply but I am pretty sure that that is not the problem because the Mbp is hooked up to an external display in dial moniter mode and adjusting the brightness does not affect that moniter also this problem is in OSX not windows

Aye, sorry I could not be of help
That is not a problem I have had.

I have no idea why but for whatever reason what you told me worked. Even though i thought it would not affect the second moniter it did. I tried pressing the brightness increase and sure enough it woke up from sleep. doesn't make any sense but thank you nonetheless for saving me extra restarts