1. Use Disk Utility and Repair Permissions.
2. Zap the PRAM. Shut down the computer, find the Command + Option + P + R keys, Start the computer and IMMEDIATELY hold down ALL four keys at once.
Keep them down until you hear the third (3rd) chime.
Any difference?
P
For now the question just about sums it up. Have restarted.That's all. Problem first noticed a couple of weeks ago.

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