Zoom extents shows much more than my drawing extents

Hi,

I am using AutoCAD 2014 (AutoCAD Electrical to be exact).  I have a drawing in which, when I choose "Zoom Extents", rather than zooming so that my drawing contents fills the screen area, it zooms way out so that my drawing contents are tiny.  When I do this, my drawing contents are displayed (very small) at the top of the window, and I see some stray marks towards the bottom of the screen.  I think these stray marks are causing my problem - zoom extents seems to be including these in my "extents".  The strange thing is, even though I have all layers thawed, I cannot select and/or delete these stray marks.  If I try to zoom in on the stray marks, they are no longer there after I zoom.

If anyone can tell me how I can get around this issue, I'd really appreciate it.

Thanks in advance,
Paul

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