Just after a bit of help, up until yesterday I have been able to install new programs and run as administrator as necessary.
Yesterday I installed an update of a game "Cricket Coach 2012" which required me to launch the program as admin, on doing this the screen greyed out and asked me if I was sure, as normal, clicked yes and the timer started ticking next to the cursor. Nothing then happened so ctrl-alt-del and looked at program running list to which it was there for a few seconds before closing.
Initially I thought the problem was with the game itself, so tried to launch firefox (specifically downloaded to run as administrator to test) and exactly the same thing happened again?
Does anybody know why or how this is happening and more importantly how to fix it? I have already created a secondary admin account to no avail!