Peugeot 106 xs electrical starting problem

First thing check the starter motor.and ALL the earths. it sounds like the starter is playing up. when it dos it again tap the starter motor and try that.and spend time checking the earth leads.

Yes tell your bro' to get his 100 notes back...

Tapping the starter motor might help - a few times. Otherwise find the small connector on the starter motor and connect a wire between plus on the battery and this connector. CAUTION; Leave the gear i neutral and don`t touch anything on the chassis with this wire, while it´s connected to the battery. If the motor works every time doing this, you may need to install a relay to activate the starter relay. Yes - it maybe sounds strange, but the switch you operate by the key (sorry what`s that called?) might be worn, and cannot carry the needed current for the starter relay. Had this problem myself in my Visa GTI and solved it with a relay.