MacBook slowly freezes before resetting

Hi there

So, my MacBook is about 6 weeks old now, and sometimes (not often, once or twice a week maybe) it will slowly freeze until I finally cannot tab between programs, and only the pointer moves, then the pointer will freeze and a shortly after the MacBook will shut down and restart, then restart again after about fifteen seconds and boot up.

I had a quick look at the logs via System Information, but nothing really sprang out at me, so I was wondering if anyone else had experienced this, or I could get some advice on what to do. If I take it into a Genius Bar I'm not going to be able to reproduce the error without sitting there all week using it, so I'm not sure what to do.

Any advice would be gratefully received!

Robsa