Yesterday, my MacBook Pro started acting up. For no apparent reason, it sort of pixilated -- though technically that's not what it did, but it looked almost the same -- and froze up. Twice, I forced it to power down by holding the power button off. Then today, it did the visual thing but rebooted. Then the apple came on, and it got about 3/4 of the way through the check and rebooted. It's looped. I tried to get it into safe mode, but it refuses. Help!