|If the computer "awakens" fine from "sleep" mode, check your settings in Control Panel - Power Options. E.g. It may be set to shut off the hard drive or the video after xx minutes.|
If it won't come out of "sleep" mode that's another matter.
A computer CANNOT stay in "sleep" mode.
If you hold down the power button until the computer shuts off, it should start up normally when you press the power button after that.
If it doesn't, you have a hardware problem.