My macbook pro is freezing and barcodes are coming up all over my screen. Once I shut down my computer and restart, it goes away, but if I pick it up, it happens again. Any ideas what the problem could be?

It seems to work fine whenever I turn off my laptop and turn it back on, but if I leave it in my book bag for a couple of hours, it will get extremely hot and when i go to open up the laptop, it is just blank. Also, whenever Im typing on my lap or seem to put a little bit of pressure underneath the computer, lots of barcodes will pop up all over my computer and freeze. Any ideas as to why it is doing this? Any suggestions would be great.