Good luck.
Sounds EXACTLY the same as a problem I had a while ago, failing starter f**ked the earths. Changed the starter and needed a freshly charged battery and a set of starter wires.
For £4 from Halfords (only place I could get them) got two (one red and one black) thick cables. One to the positive and one to a starter bolt thanks to rubjonny's advice.
Starts like a b!tch now.
