24' cinema display stuck in 640 X 480 - unless used in Apple Store!

Question

I really need some help with my new MBP and 24" LED cinema display that is driving me crazy. The first part of the problem is that when I bring my MBP out of sleep and attach the monitor, or if I simply disconnect the monitor and reconnect it without sleeping, it only shows 640X480 and no options for other display settings.
I have tried a great many things and suggestions, including deleting the com.apple.windowserver.plist files (system and byhost versions), repairing the permissions, resetting the pram. Nothing makes any difference to this behaviour.
The second part of the problem is that having decided it was the monitor itself I took both the display and the MBP back to the apple store today where it worked faultlessly - no amount of rebooting, sleeping and attaching/detaching would make the error occur. Once we gave and I got them both home again - it reverted to the previous, faulty behaviour! We wondered in the store if it was a faulty cable - but no amount of wriggling of the cable makes any difference.
When The display is correct, the system profiler shows:
LED Cinema Display:
Resolution: 1920 x 1200
Depth: 32-bit Color
Core Image: Software
Mirror: Off
Online: Yes
Quartz Extreme: Not Supported
Connection Type: DisplayPort
When the display goes to its 640 X 480 mode, the system profiler shows:
Display:
Resolution: 640 x 480
Depth: 32-bit Color
Core Image: Hardware Accelerated
Mirror: Off
Online: Yes
Quartz Extreme: Supported
Rotation: Supported
Connection Type: DisplayPort
I found a few things relating to issues with recognition of monitors when coming out of sleep - but this monitor was made specifically for this MBP, and others don't seem to be having this problem. My MBP also works fine with my DELL flatscreen display at a high resolution.
Anyone got any idea what else I can change before I have to completely rebuild my MBP. I am really confused by this - why would it insist on working in the Apple Store and refuse to work correctly at home?

Answer 1

First off, the power cable is not permanently attached to the monitor. It is a 3-pronged, grounded connector at the monitor end. I know because I just disconnected mine and freed up the entire cable. Since I'm one of those who just does stuff even when it may not always be well-advised, I can report on an experience that could bear on your situation.
I had my Mac Pro running when I reached around the back of my 24" LED display and pulled the plug from the monitor. Of course, the monitor instantly went "black". I quickly replugged it back in (no, I didn't shut anything down and risked frying the monitor). When the monitor returned to life it was "stuck" in 640 x 480 mode and I could only "restart" or "shut down" to get it restored to the 1920 x 1200 mode I keep it in.
This suggests to me that the problem lies in your cabling and power delivery system. Perhaps you are getting power surges or power spikes that have the equivalent effect of taking your monitor "off" and then returning the monitor to a 640 x 480 condition after restoring power.
If it were me, I'd try with a new monitor cable to power. I'm betting your problem doesn't have anything to do with the monitor to computer cable, but it isn't the only cable here. Something is disrupting the constant power feed and I'm betting the problem is amplified by faulty power cord. Since I just replicated your situation by literally pulling the plug and replugging it in, it seems to me that this would be a fruitful area of investigation.
Hope this leads you somewhere positive.