Bottom Quarter of Screen Stretched and Distorted

I couldn't find anyone else with this problem on the forum which is surprising since I am having this identical issue with not one, but two ACER AL1912 monitors. This problem has occurred when the monitor was accidentally left on for a length of time (5 days or more). The bottom quarter of the screen becomes distorted and extremely stretched downwards, making it impossible to use anything in that space (thus making it impossible to use the display, really). I have a two monitor set-up. This had occurred on one of the monitors in the past a couple times after accidentally leaving it on as above. I switched monitors and did enough tests to determine that the problem indeed originated from the Acer and not my computer, cables, or video card. As mysteriously as the problem occurs, a solution in the past was to leave the monitor off for a week or more (I travel a lot so this is feasible). Most of the time after it's been off for a couple weeks the monitor displays normally. The last time this happened I just made sure that I switched the monitor off so there was no future problem ... until now. Recently I was out of town for a month and a colleague used my computer set-up. You guessed it: he left both monitors on after switching off the computer and they were on for over a week. Now, upon returning, both monitors are distorted and stretched in the bottom corner. Leaving them off for an extended time is now not an option as I have a project due in a couple weeks. And with both monitors afflicted I can't just use a 'good' one. Help! If it makes any difference, I'm running these off a Macintosh G4 in a dual monitor set-up. Thanks in advance.