Identifying computers in SoM

Identifying computers in SoM

Hello,
My problem in displaying all of the computers in my workgroup by desktop central still remains.As you can see in the attached file our network shows nearly 200 PCs ,whereas desktop central can only identify a few. I am absolutely positive that they all belong to on workgroup and have the same user and password. What should I do?
I look forward to get answers from you
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