OK, so searching shows me that you have a laptop that is running Windows 7, so unless you tell me otherwise I am going to assume we are working with that.
Screen going black could be hardware or software. When the screen goes black, do you do a hard reboot, or does it come back by some other method?
One other thing is to try booting in safe mode, and see if the screen stays on.
Another thing you can try is hooking up an external monitor and see if that screen stays on.
Does the laptop's slowness and the screen going blank coincide, or can you have one without the other?
If they do, you might want to run a virus scan, but only when you can get the laptop to the state where you have a dependable display.
Are you active on the laptop when this occurs?