My Toshiba laotp's screen goes half blank help!!

Well try to boot into the safe mode.hit F8 on the startup and see if you get the same acreen.If its working fine in safe mode than you need to reinstall the video driver and that should resolve the issue.If it is still not working try connecting a external moniter.If you get the same display on the external moniter than its an issue with the video card and if you get a normal display on that than its an issue with the Laptop screen and you would ahve to get either of thses replaced by contacting the manufacturer.
Hope this helps!