How to resolve the “ADB server didn’t ACK” error? [duplicate]

Try the following:

1. Close Eclipse.
2. Restart your phone.
3. End adb.exe process in Task Manager (Windows). In Mac, force close in Activity Monitor.
4. Issue kill and start command in <sdk_folder>\platform-tools\
   • C:\sdk\platform-tools>adb kill-server
   • C:\sdk\platform-tools>adb start-server
5. If it says something like ‘started successfully’, you are good.