I was using my 2010 MBP 13 inch at work on Friday and it suddenly came up with the grey curtain, so I powered it off and then back on, and a few hours later when the laptop was just sitting there it did the same thing again.

So powered it off and back on and it did not happen again until I left work for the day.

Laptop was in sleep mode all saturday because i was busy but today (sunday) I was just surfing the net and it happened again.

Any thoughts on what could be causing it or how I can fix it without formatting? Would take me ages to get it setup the way I like again.