Q: MacBook not connecting to wifi

My MacBook Pro has never had any trouble connecting to wifi before, and suddenly presented saying that My computers IP address was in use by another device, then stopped connecting to any wifi internet. I have no idea what other device could possibly have connected to the IP address. I have restarted the computer several times, and diagnostics won't complete to try and figure out what is wrong. Initially there was a problem with the modem router and I thoughts that was the cause, but the router has now been reset and wifi works fine on other devices. The computer is currently connected to Ethernet and Internet works fine this way, but will not connect to Wifi as it did previously, to this regular home network, or any other networks (that it has previously succeeded in connecting to). Please help!