Wrong 3D Cursor - Far away from the scene I'm using Blender 2.76 under Windows.
Every time when I try to position the 3D Cursor, one coordinate is set too far away from the screen - e.g.:


I load the startup file.
I press Numpad 5, Numpad 1 to enter "front ortho" view.
I left-click beneath the cube.


I get a 'Y' coordinate of -260.91177!! - which is very far in the front of the scene.

So, it is impossible to place a new object ...
Press Shift+C to re center the 3D cursor in your scene, if this solves your problem you will want to re-save your startup file (File> Save Startup File) so you don't have to re-center the cursor every time you restart Blender.