I know this question is asked multiple time and there are some alternative answer also.So please don\'t close with some other link because i have added that link below.
I Face this problem many time i solve in my way like this and it is working
Then in command line go to your directory of platform-tools like
C:\AndroidSetup\sdk\platform-tools>
Then write following command step by step
C:\AndroidSetup\sdk\platform-tools>adb kill-server
C:\AndroidSetup\sdk\platform-tools>adb start-server
After successfully message come your adb is running now .
Now you can start your eclispe your.