Can't connect to one of my computers on the network

I go to Computer - Network and I see all the computers. From one computer I can access all data on both computers but from the other computer I can only access my own stuff but when I try and access the other computer I get a Windows Secuity which says I have to enter a password. I have the right user name and I've tried Security key, Passphrase, Homegroup key, D-Link Router password so I wonder what I'm doing wrong and how to fine my password. I can't change anything because too many computer are on the network. any ideas?

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