Macbook with 2 x 1gb simms. Suddenly won't start/boot. Says I have to restart. Thought I'd check my memory. IF I take 1 simm out it boots. Either simm in either slot will boot. If I put a simm in both slots (the way it was for 2 years) it won't start and gives me the must restart message.. Was working fine 1 day and not the next. Any ideas?