I have been reading these threads the last few days as bought one as broken for 20 quid. I found repeatedly inserting the minidisplay connector and then plugging in the usb kept the screen working for as long as the usb was connected, even if you unplugged and replugged in the disply port however......
I took the monitor apart completely. disconnected all cables and wires removed logic board, power supply and sub woofer and gave everything a really deep clean. Blowing out and toothbrush removing an enormous amount of dust from the fan. Reassembled checking all cable/wire connectors were well seated.
First time reusing took several attempts at plugging in mini display to get it to work, but then.... next time i plugged it in works straight away and at FULL BRIGHTNESS. MUCH better than before!!! I have now unplugged and replugged in mini display 20 or 30 times and it connects every time first time WITHOUT usb connected!! I have also tried every combination, unplugging monitor power while connected to mini display on macbook? Fine. Unplugging mac, then unplugging monitor from power. Turning power back on then connecting to mac? Also fine. Every variation of connection and disconnection. I would thoroughly recommend just giving the unit a thorough clean and checking ALL connections to logic board, power supply, speakers, display, and the two heat sensors. Maybe this won't last long, but maybe it will!