How to wakw up my laptop after it has gone to sleep and cut off the display?

Can't someone please help me? I have a new Acer Aspire laptop computer, blah, blah, blah. How do I wake it up after it has gone to sleep and cut off the display? When I open the lid after a lengthy absence the display is black. I DO NOT know how to wake it up properly. I've tried doing nothing but opening the lid and waiting, and waiting, and waiting...but nothing happens. So I give the power button a quick little hit and the next thing I know it's shutting down. Please help. IDK. It's not like I'm a novice, I've had a personal computer for six years and a laptop for five years, but this is my first Acer and my first Windows 7.