Oh oh! I've had this happen to me before. It's really annoying.
Eh, if I remember correctly.....
Start >> Control Panel >> Display >> Settings >> Advanced
There should be some tab that allows you to rotate the display screen back.
I've never tried this but this post suggests using some type of hot key.
http://engtech.wordpress.com/2006/08/01/stupid-windows-features-monitor-display-turns-sideways-or-upside-down/
Ctrl-Alt-Up - right side up
Ctrl-Alt-Right - 90 degrees
Ctrl-Alt-Down - 180 degrees
Ctrl-Alt-Left - 270 degrees
(If that doesn’t work, try Ctrl-Shift-R)
If the hot keys work, pls let me know.
Hope this helps.