my car completely stalled at 30mph...everything stopped and would not restart on 1998 Jaguar XJ8

after starting car up went about 4 miles radio went off and on then completely went off..windshield wipers stopped...transmission fail warning came on messages then completely stopped had to pull off road with everything dead...would not restart..had towed home on flatbed..had to over ride gears to neutral to get on tow...???? I just purchased 1 week so discouraged...ty for any help

Asked by for the 1998 Jaguar XJ8