It was a 17 inch MacBook Pro and on removing it from its home I saw the battery pack was bursting open. I removed the battery and it expanded more and more. Took it into the Apple store - they said many were being returned so I bought a new one (£99!) and it's now working fine.

But this is obviously a common problem and I suspect a potentially dangerous one, especially for those with only one laptop and less regular back up and copying/duplicating habits.

New technology in many ways not perfect.