I hear about these often and they can happen for a variety of reasons. The trick to resolving these issues is to find out the answers to some questions.
Question and most common reason(s):
1) Is it drawing specific? If it is, then clean up the drawings and xrefs. This can be tricky because if you don't clean up the Xrefs first a reloaded Xref may bring the badness back in. Also, a layer that is turned off or frozen, etc won't help during a purge.
2) Is it machine specific? if it is, then disable other programs from running before you run AutoCAD, ensure you have the most current Autodesk Recommended/Supported graphics driver for your version of AutoCAD.
3) Is it specific to your Windows login? If it works logged in on the same machine as a different user then you may have a bad AutoCAD or Windows Profile.
4) Is it specific to your machine only? If it is, then you may be looking at a hardware problem, problem with the Hard Drive or Windows or AutoCAD install.
If you're having problems narrowing it down, or have it narrowed down and you're unable to fix it, give the National Support Center a try. We work with these issues quite often. We can be reached at 800-808-7645
Ciao for now!