First... It sounds like the rooting altered your phone a little more than you wanted. The first thing I would suggest you try is a "hard reboot". This may be all it needs. All you would do is turn it off and pull the battery. Leave it out for about a minute (maybe two). Put it back in and restart the phone.
Second ... Have you used something like Root Explorer or ES File Explorer or are you using the built in file manager? If you are only using the file manager it came with, I would suggest you try those apps.
Third... If that doesn't work, then I would ask... Do you actually have any files on the Internal Memory you need? ...I ask because if not, then a hard reboot would be what I would try next. However this will remove any apps and...