changing screen display size - not resolution

2010, 27" imac, os X 10.6.8, 8gb ram, 4 2tb externals
OK so here's the problem:
Went to bed last night and all was fine. Wife borrowed the computer. Woke up this morning and the screen - including top menu bottom pop-up menu and sides have become extended beyond the viewable area of the monitor. If I move the mouse all the way to the left, it pushes the icons for the external drives off the right side of the screen. If I push the mouse to the right, everything left of the "view" menu gets pushed off the left side of the screen. Similar for top & bottom.

So far I have:

• reboot - no effect
• reset the display resolution - no effect
• reset the system preferences through time machine to 1 month ago - no effect

Any suggestions before I run a complete backup off time machine? (reluctant to do this as last one took 14 hours)
windows monitors usually always have a menu for these adjustments (size,position,keystone,pincushion,etc) but can't find any info on such a menu on the imac. Already know what Apple customer care will say, they seem to have 1 solution for every problem "reinstall the operating system and if that doesn't work, bring it in.".

 

Awesome, thanks so much!