Power loss when Trigger pressed

Maybe someone has a proper idea.

Bought my old D70 back of a friend of mine, because it was my "first" DSLR, and went defect - So she couldn´t use the cam anymore.

The following problem occurs:

When pressing the Tripper die Mirror isn´t flipped but a weird mechanical sound occurs. Some "grrrrn" short sound.

While pressing the trigger the inner Display fades like a motor drains to much power or a capacitor doesn´t give the propper energy.

I fist got a new accu because that might have been a defective cell problem, but this wasn´t the case.

Opened the case but can´t see any "obviously" damages at the main cap or the onbord mini-caps.

Btw - the shutter shutters. Also in the main menu i can´t select the "mirror" option. it´s grayed out, regardless the camera mode and even after resetting to factory defaults.

Btw (2) : Where do you folks get your replacement-parts? :) (I´m from germany - The only solution would be the Nikon Service-Partners i assume... - Do they sell repair parts to end-customers?)