When the Optiplex 7020 you got was purchased it was selected to not have Wifi module included, simple fix with either you can buy a USB WIFI Adapter or if you want something much stronger and better, get a PCI-Ex1 Wifi Module
It is probably a diagnostic code or it is in a sleep state, search up your model's manual on Google. Mind if I ask by blinking does it blink than stop or just continues blinking
