Right click on your desktop
select Graphics properties
within that you would get 4 options - select the Hot keys option
Within the hot keys check if there is anything written for Screen - 'Rotate to Normal'
The option present is the way to return the screen to normal
If no option is present then take our mouse over there and you will get a drop down menu
Selet the option from that and do the needful - ur screen will be okay.