Thanks Sean,
I've had a look at the TC settings dialog and tried to keep it as simple as possible. I also had a copy of LR 4 on the hard drive so have trashed that also incase of any conflicts. LR seems to be running ok now but as said it's an intermittent problem.
I also have a copy of Capture One on the hard drive so am going to uninstall that also in case it is trying to launch.