I have found that the problem is related to Internet Explorer 6
I have not been successful at changing various IE6 settings and
eliminating the problem.
Therefore I have chosen to take the following actions hoping to
resolve the problem;
Remove PowerDesk Pro 6 and install version 5 which I have
Install Internet Explorer 7
If this doesn't work I will have to revert to restarting my computer as a
means of reactivating Power Desk when it does quit on me.
I will keep looking for a final solution.
Thanks to those who offered possible solutions.
When I get time, will try safe mode to try to isolate the problem.