I previously developped Android apps on Android Studio . Everything works fine.
I work on real device, and Android Studio recognize it without issue.
Suddenl
open cmd and type the following command
netstat -aon|findstr 5037
and press enter.
you will get a reply like this :
TCP 127.0.0.1:5037 0.0.0.0:0 LISTENING 3372
TCP 127.0.0.1:5037 127.0.0.1:50126 TIME_WAIT 0
TCP 127.0.0.1:5037 127.0.0.1:50127 TIME_WAIT 0
TCP 127.0.0.1:50127 127.0.0.1:5037 TIME_WAIT 0
this shows the pid which is occupying the adb. in this 3372 is the value. it will not be same for anyone. so you need to do this every time you face this problem.
now type this :
taskkill /pid 3372(the pid you get in the previous step) /f
Voila! now adb runs perfectly.