If you are using fixed IP, then high chances are that two PCs were set to the same IP.
However, if you are using dynamic IP, the following describes a scenario for it.
There are two WiFi networks in the environment.
1.) PC-1 connected to Network-1 and received IP-1
2.) PC-2 connected to Network-2 and received IP-2
3.) Network-1 restarted
4.) PC-2 restarted
5.) PC-1 connected to Network-2 and received IP-3
6.) PC-2 connected to Network-1 and received IP-1
7.) PC-1 disconnected from Network-2 and connected to Network-1 and received IP-1 because it didn't restart itself --> IP conflict detected.
The solution is to disconnect PC-1 from Network-1 and reconnect again.
Note : It is not always true that this happens because someone is trying to hack you by mimicking the IP address of your PC - especially if you are home alone connected to your own routers.