It could just be the polyfuse protection. The V2 has a polyfuse that protects it from over-current conditions. That fuse will automatically reset once the over-current condition no longer exists. Although after plugging it into different vehicles it should have been OK. It may also bee the RJ45 connector has cracked solder connections to the main circuit board. Or like you thought, it may be a faulty OBDII cable. Does it power up OK via the USB connection?
If you want it repaired contact SoCal Diesel, they repair FlashScans. Their contact details are here:
http://www.efilive.com/distributors
Regards
Paul