I just went through the same problem last month. I could not get the usb Proprietary plug to stay in the unit. It would just fall out. pressed it in as hard as I could to no avail. Needless to say it would only make sporadic contact, so would never connect to computer. Just a junk connector on a otherwise decent player that makes it worthless.
Sent back for refund.
Any X7 lovers think it is worth another try? I know that this is a known issue with these players. How about someone that has had one for a while, does the usb cable still work? Will it last through 200 to 500 connections? ( usb's have a rated life expectancy).