sounds like a graphics card problem?? where's the big guns.., Gster, some guy, and a few of the others know much more about this stuff than me.
sounds no good to me. Id first dump the preferences (just rename your documents/maya/preferences to 'old preferences' and a new set of preferences will be made next time you load the app.
id try a repair.., reinstall the app!
if you are using maya 8.5 I wouldn't be surprised if its a bug in the app. seems full of them.., have you checked the service pack thats available for 8.5. (personally I think 7.1 was the maya pinnacle but Im no maya expert, just a hobbiest so all the subtler tools are lost on me.)
hope someone can help you with this.., I have had this problem too but usually I just reboot and all is fine.
try dumping the preferences, that will reset EVERYTHING (well, most things).
take it easy and life will be easy