why does stop light flash?!?

My peugot 206 hdi has a red stop light flashing and I have lost power to my spedo and instruments! it's working fine apart from that, just had a full serivce last week and no problems, radio was left on for a while by accident and now stop light flashes all the time! is there some way to reset this? should i take it for a long run to recharge the battery?