could be your ign. lock going. in my 93 lwb i had issues were i could not turn the key sometimes and my wife and r 1yr (at time) almost got stuck in a parking lot in the winter. sometimes it would turn great and then the nest time it would not turn at all. i had something happen like your talking about to. might not be and only the ign switch. just a thought.
good luck
http://www.roverparts.com/Parts/STC1436G.cfm
