Just about daily my new MacBook (less than a week old) gets a message in 6 languages telling me I "must" restart my computer. the entire system is completely frozen, and all i can do is press the power button until it shuts down. it seems completely random. first time it happened when i plugged in an ethernet cable, but that's not reproducible. this morning i just moving the cursor when it happened. defect? should i send it back?