Its been a day for breakages today. Firstly last night my PowerBook began to slow down and when I did I system profile only half of its memory was registering. After testing the individual memory modules successfully I put the RAM back into the machine and everything came back up as normal. I was hoping the problem was solved but then this morning the laptop froze with what looked like a kernel panic.
After rebooting only half the memory was visible again which was a sign of definite motherboard problems. Fortunately I had invested in a 3-year AppleCare protection plan
when I bought the machine so it was just a case of backing everything up and taking it down the road to the local Apple Centre.