External monitor randomly lowers resolution adds black borders

Okay this has been driving me crazy long enough.

I have an external monitor who's resolution is 1920x1080 60Hz. My MacbookPro Late/Mid 2010 has been able to work with the monitor and resolution since I've owned it. However, this past month or two the monitor's resolution would seem to reset itself to 800x600.

The reset seems to happen sporadically, usually when coming out of sleep. I also experience the monitor going in and out. I've already replaced the Mini DisplayPort to VGA adapter.

Here's a screenshot when the monitor acts up. I can't get rid of the black vertical borders that magically appear nor can I select 1920x1080 as an option:

Sometimes after several restarts or plugging/unplugging the adapter, the monitor will fix itself. I have no idea what is going on, it is very frustrating.

I forgot about this question, but I eventually did find an answer.

It was a bad cable. The VGA cable was faulty (the Mini DisplayPort adapter was fine actually) - once that was replaced, everything worked fine.

I'm not sure what's the root cause of the issue. However, have you tried adjusting the 'Underscan:' toggle in 'System Preferences' > 'Displays'? This should allow you to zoom in and out of your display. To get rid of the black bars, you want less underscan, so zoom out (move the handle to the left).