I had something very similar on a B7100. After I'd fitted a new starter (!) it turned out to be a broken cable between the battery and starter solenoid. Cable looked fine, but starter would click and jam, then all go electically dead for 5 minutes, then you could do the same again having freed off the starter. The cable was being heated by the current and separating at the break, then cooling and re-connecting! A new cable from the local motor parts shop solved the problem.
Meopham Trader, May 2008