Turns out it was a rotten power cord. When I changed the battery I had to bend it. I likely broke a lot of the cables inside apart cause they were rotted.
This one is baffling me and the mechanic.
New Holland 4635, have never really had much trouble with it.
When to start it a week ago and would quite turn over fast enough so boosted it and away it goes.
Drove for a while, shut it off and put battery on charger for a few hours.
Wouldnt start...