golf gti wont start

trying to start the car today but when you turn ignition on and go to start the engine all lights on dash go out and the voltage gauge drops right down and it doesn't turn over
any body got any ideas have cleaned all battery leads got 12v going down to starter but nothing battery fully charged and doesn't drop when key is turned to start.

Very odd, id be looking to the battery but youve check that

Could be the started broken and earthing out everything?

going to test the battery and starter today

Check your earth straps and clean them up if necessary.

all sorted now thanks