Is this my 600 LMT Navman already charged in build or have to charge from computer?

Can you charge it from the cigarette lighter cord? I'm thinking some GPS will neither charge nor run from a USB power source. Garmin, I believe, uses USB only for updates, not as a power supply.

Connect a usb cable at the back of the unit with the computer for hours till it is fully charged.

Check the wattage output on the charger. It may not be the correct charger that you have for the device. If this problem persists, carry your device to a cell phone store preferably in a mall, then find the one that fits your device and purchase the correct charging cable.

get a usd

screen shows computer to navman all the time

Have you tried another charger? its likely charger fault or gps internal short circuit. does gps unit switch on at all?

Your Navman will not run in car unless the output on the charger is 1000ma or 1a. you need to buy a genuine charger, motorola phone chargers do not have the output to run the unit

The problem is that most of the chargers have the output of 5V/0.5A. The charger for NAVMAN (C30 in my case) has 5V/1A. And that is causing the trouble. The GPS is undercharged and is switching off itself. Buy one which specify the output power: 5V/1A. Hope I solved your problem

if you have a motorola razr the same charger works

that is probably due to the battery being totaly dead,
try using a mobile phone charger (nokia),
usb is for data transfers.