'another computer on the network have the same IP address' question

I am a bit worried about this hope someone could answer these question PC 1 is connected through ethernet cable and PC 2 is connected through wireless. So PC 1 is connected but PC 2 isn't so I turn off and on the router. When the router is on the message 'another computer on the network have the same IP address' appear on PC 1. I decided to turn off the wireless for PC 2 and turn off and on...