Uncommunicative

[Zipporah Schumaker]

Adjective: jack shit and/or gibberish comes out. endless; almost seemingly pointless chatter that instead of reducing a situation [on the contrary] ESCALATES it and leaves one feeling extremely childish and plain DUMB for not being able to get oneselfs point across.
[tongue-tied], speechless, [wordless], feeble-minded, silent, soundless, dimwitted, inarticulate...

[Cami]

(of a person) unwilling to talk or impart information.

[Gregory]

not willing to talk: