Frozen mouse then computer gone off! Help

[Squiz]

I was helping my son with his homework on the computer- younger son was trying to plus something into the USB port the wrong way around- when the mouse cursor got stuck in the centre of the screen. I tried lots of things to unstick it, rebooted computer, switched it off for a while but nothing has worked. Now the screen does not seem to be connected to the computer - it just goes to powersave mode and will not come on. What's happened? Can anyone help - I can access the laptop for helpful suggestions, thanks.