Marc, it's just possible that your BIOS backup battery (Brit: pile) is dead. That's the one on the MOBO that looks like a coin, about 1-1/2 inches in diameter. It's dying throws creates symptoms similar to those you describe. It's a rare occurrence - I have only had one die in all my years on PCs but the symptoms were very similar to yours. It's an inexpensive test to try, under a Quid.