I was having issues viewing part and assembly previews in my Windows 7 folder preview panes. I scoured the forums and asked my reseller tech support, but no one could find an answer for me. Below is the answer on how to enable the previews.
I like to run with no Visual effects turned on so this is what made my Preview pane Part/Assembly previews dissappear.
Note: in order for solidworks to render part previews you must have the "Show thumbnail graphics in Windows Explorer" checked in SolidWorks under Options>System Options>General
1: First go to your "Start" menu and right click on "Computer".
2: At the bottom of the menu select "Properties"
3: From the choices on the right hand menu select "Advanced system settings"
4: The "system Protperties" window will pop up. Make sure you are on the "Advanced Tab".
5: Click on the "Setting" button of the "Performace" field. The "Performance Options" Window will pop up.
6: Make sure you have the "Visual Effects" tab selected.
7: Find and check the "Show thumbnails instead of icons" box.
8: Go back to Explorer and your part preview will be shown in the preview pane.