Fuel tank sender issues

Hi folks,
Can you offer any advice? I had to drop the gas tank to have it repaired. To get rid of the vapour I filled it with water and left it till I could find someone to weld it.
I then refitted the tank and found the gauge had stopped working. I earthed the power feed and the gauge rose. So assumed the sender was faulty. Well I replaced it fitted a new earth ( just in case ). Low and behold the gauge still is not registering ! Oh and now the car has cut out and won't start !! Ideas ?? How it check it hopefully without having to drain it again
Thanks