I think we have all experienced some quirks from ArcGIS. However from time to time it may be quirker than normal and no matter how many times we restart Arc or reboot our computer it continues to act wierd. One of the more common causes of this type behavior is the Normal.MXT has become corrupt.
The Normal.MXT is the default template used by ArcMap any time a new map is created. It also stores most of your display customizations such as what toolbars are on and where they are docked. So the Normal.MXT is changing often which is why it gets corrupted. These setting are also applied to existing maps which is why they will act funny if the Normal.MXT has become corrupt. So what is the fix for a corrupt Normal.MXT?
The fix is easy. You just delete the existing one making sure ArcMap is closed. The next time you start ArcMap, it will recreate the Normal.MXT from stratch. So where is the Normal.MXT stored? It is stored in your user profile which is normally located on your local drive at c:\documents and settings\%username%\applications\ESRI\ArcMap\Templates\. There is one draw back to deleting your Normal.MXT. You loose all your custom settings. So how do you avoid that? Well that is simple. Make a copy of your Normal.MXT once you have everything set the way you like it. So when ArcMap starts acting wierd even after a reboot, all you need to do is copy your backup Normal.MXT over the active one. This way you keep all your customizations while at the same time getting rid of the corrupt file.
ArcCatalog also has a default template, Normal.GXT. It is less common for this file to become corrupt since there is less you can customize in ArcCatalog however it can happen. Like the Normal.MXT, the Normal.GXT is stored in your user profile and is recreated on the fly by ArcCatalog if it is missing.
Hopefully this proves helpful. I know I have used this tip often.
Tripp Corbin, CFM, GISP