My MBP 2011 has trouble waking from sleep mode

Just recently my MBP has been having trouble waking up from sleep mode. When I open my laptop it usually just wakes up, and right now it will flash my screen as though it is going to wake up, then the screen goes black and thats it. If I push any button nothing happens. If I press the power button and noise will happen. I have to hold the power button for about 20/30 seconds before it actually turn off. I then turn it on and everything is fine. I am not sure if I am the only one having this problem or if anybody knows why this is happening. Let me know if you have any info or if it is happening to you as well.