Garmin nuvi 760 won't turn on

SOURCE: garmin nuvi 200 route calculation problem

Sounds like a major software failure. . .

Hold a finger on the upper right corner of the screen while powering up the unit. This should do a master reset.

The go here to download an update.

SOURCE: installing free maps

thanks

SOURCE: garmin 760 is stuck on enabling bluetooth

refer to this link

http://www.garmin.com/garmin/cms/site/us/lang/en/searchsupport

SOURCE: garmin nuvi 760

Go to tools-settings-language-voice and make sure it is set to "American English-Jack (TTS) or to American English-Jill (TTS)

SOURCE: Garmin Nuvi 760

Sounds like you both have a battery problem. I experienced a similar problem when trying to charge via the USB-cable connected to my computer.
Ended up buying an original charger (expensive) and the charging went smooth.
The car charger should in any case work fine, so probably your battery is not very healthy.

Try holding your finger on the battery symbol for about 10 sec. The unit will then switch to a technical page. There you can observe the battery and charging voltage. When I plug in my computer USB-cable, I read around 4,4V and that is not sufficient for charging my battery.
When connected to the original charger, this voltage rises to about 5V which gives a nice charge. When unplugging charger, the unit displays the battery capacity. If the charging voltage is OK, but battery capacity drops quickly after you unplug charger cable, the battery is probably bad. (Of course you have to charge is for some time) I think around 4V battery voltage give 100% capacity. 3,9V gives about 90% capacity.
This will not solve your problem, but can give you an idea about what is wrong.
Good luck.