Jock1e, Thanks for your replies. I had a look in Control Panel and found:-
Adobe Flash Player11 ActiveX installed on 17-02-13 and JavaTM 6 update 37 installed on 11-11-12.
I uninstalled the Flash Player (as it was the more recent install) and went to these forums but the problem is still occurring. I'm not sure if it is worth uninstalling the Java update as it was installed some 3 months ago and the problem appeared only a couple of weeks ago.