Well, I upgraded my PC to the latest version of Ubuntu, and it has been a bit of a pain in the backside. I had all the problems with the Nvidia driver I had with earlier versions, but yesterday, things went really pear shaped. I came home to PC at the login screen, and logging in resulted in - the login screen. So this evening spent a load of time trying to figure out what was going wrong. Obviously X or the gdm wasn't starting up, so I tried to boot the machine to a shell, but even the kernel failed to boot. OK, I thought, recovery mode, but even that wasn't working correctly. Then I noticed a No space left of Device error message. AHHHHHHH. The main hard drive was full. So, I booted Ubuntu from a CD, and spent some time deleting files, and found a backup file that for some reason was on the hard drive, rather than the USB backup drive.
Rebooted the PC, and hey presto all back to normal, so my earlier complaints the KK had knackered my PC were unfounded - the problem was of my own making - I need a bigger hard drive!