When working with my Toshiba laptop after a few minuets the screen goes black and the machine freezes. What could be the problem?
Agree with Frank that the screen going black points to the video card. I've seen overheating issues often and usually that's a freeze or a complete shutdown. A black screen points toward video issues.
Quick test of course would be to swap out the video card for a new one. But first, since you said it does start up, I would launch it in safe mode to see if the behavior still occurs - you never know sometimes what could be triggering something like this and safe mode is a quick way to cancel out software being a cause. Once you've confirmed that it still happens, I'd start looking at the video card as the next point of failure.
it could be the video card over heating ... have you checked to make sure the vents are clean?
I agree with Frank. If you are certain it freezes entirely, my first guess would be a thermal problem too.
If you are not entirely certain, just start playback of e.g. a movie or music and wait for the screen to go black. If the audio continues it's obviously just the screen: try unplugging the power plus taking out the battery and then back together.
Also, if it doesn't freeze but the screen goes dark but not quite as if the device was power off it might be an issue with the LCD backlight (assuming it is of that type).
I agree too. If it's a matter of (more or less) fixed time from startup, it's most likely to be a thermal problem.
which version of windows you have.
1) Go to run and type cmd, right click on it and choose run as administrator
2) on the cmd screen type: sfc /scannow and hit enter, wait the scan to finish
Windows 8.1, Windows 8 or Windows 7 hangs or freezes
open Event Viewer and check Error code