I also have a digitizer that for no clear reason is not working. I recently purchased a used Droid 3 with a cracked screen but in otherwise perfectly working condition. Ordered a new digitizer, took it all apart and replaced the cracked one, phone starts fine but I have no touch control (I can power off the phone using the keypad), took everything apart again to make sure all connections were secure, put it back together, still nothing...
disassembled the phone for a third time to re-install the cracked glass, still no touch control (phone boots fine with keyboard)... I only see one connection between the digitizer and the ribbon on the back of the lcd, and one connection between that ribbon and the motherboard, all connections are tight and I see no damage anywhere... I'm lost, I'm curious what you could be doing to make it work sometimes and hope any solution you find can help me as well, Good Luck