1993 Rover in a coma... help!

My 1993 Range Rover classic quit on me about 6 weeks ago, my mechanic hasn't had much luck with it and I am desperate to get my wheels back.

So the story is, she was running beautifully, started on the first time every time and had a brand new battery. I stopped to get gas, but when I tried to start her up again nothing happened, the engine didn't turn over or do anything for that matter. The lights didn't even dim out when we tried to start it so we knew the battery was still fine. My dad came out to help me and tried a bunch of stuff but nothing worked so we ended up getting it towed.

My mechanic has traced all the wiring and hasn't found anything wrong. I was hoping for some help, I'm in desperate need for help 'cos I love that car and I do not want to trade it in. Any suggestions you guys could give would be great.

Thanks