when trying to start engine , the battery gauge goes backwards, and won,t start?

Answer 1

Your battery is discharged or the connections at the battery need cleaned.
Try jump starting your car with a good pair of cables.
Once running check the voltage gauge, it should read 13.5-14.5 volts. (if the voltage is low 12volts or less the alternator is not working)
If the voltage is very high 15-16 volts, your battery has an open cell and is bad.)
While it is running drive it to a Auto-parts or Auto-service store and have them check the Battery and charging system.
Do not shut it off prior to having the system checked, unless you are somewhere you can get it jumped again.
The heat is killing many batteries.
If you have the tools clean the battery terminals first. They are often the cause of this type of problem

Yours:Grumpy

Answer 2

Whenever there is a load on the battery that the alternator cannot maintain, the gauge will show a discharge. If the engine is not running, the starter will draw on the battery showing a discharge.
As for the no-start,
1) Is there fuel in the tank?
2) Does the engine crank over?
3) Is there spark out of the plug-wires?
4) Has the engine thrown it's timing belt?
GOTS TO HAVE MORE INFO!!