Problems starting please help!

Hi,
I have a P reg discovery TDI , I changed a fuse in the drivers side panel,when I tried to start the car after there was no heater plug light,I changed that fuse (i may have disturbed it) the light then came on, but the car would only turn and NOT fire,its been like this since,it turns won't fire until battery is flat,then IF it does start,once warm it starts 1st turn everytime,leave it overnight and we're back to the same problem turns won't fire, any ideas guys ????

i had one that used to do that, a touch of easy start and off it went then was fine all day. Changed a shed load of thing and still the same till one day the starter packed in, proberbly due to all the extra hammer it was getting in the mornings. Replaced started and it started first time every time