Dell Inspiron 660 on Windows 8

Hi,

I've recently bought a Dell Inspiron 660 running Windows 8 which has been working well. However, in the last week, it's been randomly switching to just a black screen and no keys / mouse etc have any effect. The only solution is to reboot, which works. There seems to be be no consistent pattern about when it does it; i've been working on Word, on games or sometimes, it just does it when the computer is on and left alone.

Any ideas ?

Ta