This is an odd one. After a Dell U2412 LCD had been placed on its face to connect cables, the screen became locked. After some research this apparently happens when the MENU button is held in for 15 seconds. So monitors like the Dell E228WFP, P2210 and 1701FP can be unlocked by holding the MENU or SETTINGS button for 15 seconds.
The question is, what about the more expensive programmable LCD’s like the 2412… they have four programmable buttons. The answer is to press and hold the BOTTOM button (not the power button) for 15 seconds.