First, I would never do a save to a floppy from an open drawing - you're asking for problems - AutoCAD doesn't like to work that way. Always do a save to a hard disc first and then copy the file from the hard disc to the floppy once the drawing file is closed and only use the floppy as a backup or for tranferring the file to another computer.
I find the a setting of 2000 (max is 20000) is sufficient for most purposes for arc smoothness.
Also a setting of 5 for rendered object smoothness (max is 10) is sufficient most of the time.
Of course you can increase these values from what I normally use but then you put extra strain on your system resources.
Try Photo Raytrace instead of Photo Real as the rendering option - it's much faster with only a marginal loss in render quality.
When you reopen the drawing check to see all layers are ON and not frozen.
I have found that sometimes when materials are attached to a model it changes the line colours of the layers as viewed on screen and if the screen background is set to black it's sometimes difficult to see the model against the background. Setting SHADEMODE to 2D helps to view the model in this case.
Have you tried selecting everything on screen to see what is there?
Have you got the latest video drivers for your graphics card?