WiFi connects to 169.254.* only with 27" i7 iMac

I work on 2 locations, and both locations have a TP-Link router that connects to the modem. 2 iPhone's, 2 iPad's, MacBook Pro, older iMac all connect fine with WiFi, but my 27" iMac gets a self proclaimed IP adress 169.254.* and subnet 255.255.0.0. Tried manual instead of DHCP, doesn't work eighter. Tried the Pram solution, nothing. Tried a lot by now and nothing seems to work. With ethernet cable it works fine, but Wifi no go. Anyone tips?