diagnosing db link errors

Yesterday I have no problem using a database link. Today I am getting tns
errors. I have no access to the DB server (its owned by a different vendor).
I have to go through channels to contact them. Is there anything I can do to
diagnose whether its a network issue or the database/server is down. This is
the oracle error I got.
ERROR at line 1:
ORA-12560: TNS:protocol adapter error

tried tnsping and I could not reach the box. I don't have alot to go on, but
I don't want to sit around and wait for a response.

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