Found the answer elsewhere. It confirmed my suspicion that the problem was with the power saving divices(monitor off, screen savers etc) which can effect other functions if they go awry.
I normally leave my PC on and lately after being idle for a few hours a white rectangle appears with CLOSE in the centre. After clicking it off I cannot access anything, can't even connect to my server. I have to close my PC and reboot to get it back to normal
Anybody any ideas?