Unable to list the servers in Opmanager .My prob is not listed in central server

Unable to list the servers in Opmanager .My prob is not listed in central server

Hi ,
 
We have 2 prob and 1 central server. My one of the prob was down on last month .But my opmanger working fine using the one of the prob.
 
now my another prob also down .prob also working fine and central server (web server ) also working fine.
 
Now the issues was all of my server was not shows in opmanger .
 
 

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