I was just about to ask weather anything happened on the laptop screen, but
It sounds like its a memory or graphic card problem. It might just be that the memory/graphic cards need reseating, or it might be that they have become faulty.
I've just had this with my desk top, first If I knocked the the tower everthing would cut out and then reboot, checked all my connection, but the problem persisted. Then I would have trouble booting, then wouldn't boot at all, reseated graphic card to no avail. Then I reseated my memory card and haven't had a problem since.
Don't forget that it has been really hot lately, and this could have caused the cards to work loose due to expansion, more so with laptops due to being moved around.
If this doesn't solve the problem, try new memory first, this may have become faulty.
I'm suprised that if the shop couldn't find the fault, and the lap top is under a year old that they haven't replaced it?
If you feel that this haven't solved your problem post back with details, make, model i.e p4 2.ghz ect, and the operating system you are using. The more details here may make it easier for someone else to give a better ansewr.