It sounds like you are experiencing some type of corruption. There are a couple of things you can try, the first is to delete the cache file. This can help to undo any problems that are associated with that file.
The second thing to try if deleting the cache file does not fix the problem is to delete the config folder. This will remove all of the installed extensions though and should only be used if you cannot resolve it any other way.
Here is a link to a troubleshooting page with instructions for both of these: