Apple logo screen returns with diag mode attempt.

Tried disk/diagnostic mode and won't go beyond the apple. I hear no clicking, chirping or whirring when I do a reset, though a reset makes the logo disappear for a moment before returning.

Checked all inside connections and they seem to be well attached. The last time, the battery was dead when I put it back together, but was coherent enough to put a message on the screen of 'please wait, very low battery' so is that a hopeful sign of something working?