My TomTom 920 turns on in my car but when connected to the car charger the charging light does not come on and the device displays a bottle symbol and turns off

It appears that the battery will not hold a (good) charge anymore. If it is still under warranty, contact TomTom to address that problem. They may replace the unit for you.
It is not unusual for (rechargeable) batteries to loose it's capability to hold a good charge if it is plugged in (to a power source) all the time, even while it is not in use.

The batery is finished, even if you plug it in the cigar lighter and the green light goes on, your TOMTOM will still not work when the batery is dead..get one real cheap on ebay.
Good luck

try restting your 920

1. Check that the battery is charged properly.
   Charge your device for at least 2 hours before trying to turn it on again. Make sure the charging light on your device is on.
   
   
2. Remove the SD card
   If your device uses an SD card, remove it.
   
   
3. Reset your device.
   Use a straightened paper clip, or something similar, to push the reset button for 15 seconds.
   
   
4. Turn your device on.
   Press the On/off button for at least 5 seconds.
   
   
5. If your device uses an SD card, insert the SD card.

if it is not charging in the car then the socket in the car is dead, blown fuse or defective socket..

Well this is a guess here.
Are there any lights on the unit at all?
when it was on the charger did it light the chatrge lights ( blinking). Try putting it back on the charger and seeing if it turns on while connected ( may take a few mins before it will) If it does turn on wjhen on charger I would suspect either the battery discharged instead of charged, or the battery collapsed.
It needs to be sent for repairs.

If it is charging via a USB connection on your computer there is nothing wrong with the TT. It doesn't matter if you are trying to charge via USB, mains, or car charger the connection is the same for all in your TT. I would look elsewhere for the problem. More than likely your car charger is faulty.

Mine does the same, the light comes on on the charger, but not on the TomTom unit itself. There is clearly a loose connection in the cable somewhere as you can twist the flex and make it work, although this is not very reliable.

I just use a USB charger from an old phone instead.

using TT home check that you still have the symbol you want installed on the TT. I had a similar problem where it would seem to forget what I had choosen on occasion and sometimes I had to use TT home to check and re-install. problem itself seemed to just go away. (Guess it got sick of me telling it LOL)

If its still under warranty, get it repaired.. it sounds like hardware problem. Of course, you'll need to contact TT for repair options.

The power light only shows that power is getting to the TomTom. It proves nothing else and doesn't even confirm that the internal battery is charging. If you have tried a reset ( by inserting a paper clip into the reset hole at base of your TomTom and that hasn't worked then it's likely you have blown internal components . Usually caused by faulty charger. I hope the reset works ... good luck