Desktop is smaller than screen

Do you leave the power on of the monitor and just let it blink itself off to sleep?
If so, avoid, it, when you hit the sack and finally feel really sleepy, leave the PC on but manually switch off the monitor.
Leaving it on like that and not being used for so many hours, sometimes causes this in monitors, and when they come on the comp feels like reducing the resolutions and windows.... dunno, but it's certainly something with the monitors.
I used to have this problem with my CRT Samsung DynaFlat screen......