Lupo 3L does not start

Hello I have bought a Lupo 3L bj.2000 as a second vehicle. Km stand : 220tkm According to the previous owner complete mechanics of the transmission new. In the engine compartment is also to be seen that the tub is new. Now to my problem: I turned off the car and forgot the radio on. After about 3 hours again ignition on made no murks. No organ nothing at all. Starter has tension, light machine is also in order. My workshop tells me he would not have much idea about it but would look at the Type the gear control unit. What went very short for about 1 second that he has nailed that happened 2 times. I come from Salzgitter and would be happy to help you with any kind of help.