Try looking in control panels. If you have intergrated video, it's probably Intel, look for a control panel that sounds like an Intel graphics controller. Mess around in there and see if you can rotate the screen back.

If it's Nvidia or an ATI card, go into the display control panel, then the last tab "settings," then the advance button below. Somewhere in there you'll find all the options for you video card. It's different for ATI and Nvidia, so I can't instruct you further.

Though, with a nvidia card, I find just clicking the tab at that point that says your card, then with the new options that popped up you'd look for nvrotate, which lets you rotate your screen.

Another option is if you reinstall the graphics drivers it might default things back to low res rotated back to normal.