I know this is an old question but I just found this forum so I will add what I know for future inquiries.
Some electric tools (and I think Bosch jackhammers do) will stop on there own when the brush set wares out in order to protect the commutator bars.
Get A new set of brushes installed and it should start working again.
Good Luck!
G.R. Ronan, July 2011
