Looks like someone stole your "shellnew" entry for text files. Try diving in the registry, HKEY_CLASSES_ROOT, and find the ".txt" extension. Inside that key should be another key called "ShellNew". If it's not there, make one. Now stay over "ShellNew" and make a string called "NullFile". Leave it's value data blank. Restart just in case, and your missing Text Document should return... in theory.
For some reason, it didn't work when I did it in the registry. I don't understand why it didn't work...however, I did solve the problem...and maybe it is the same way, but I tried it both ways and this is what worked...
Open a folder and go to Tools > Folder Options...
Under folder options, go to the File Types Tab...click New...enter TXT and click the Advanced Tab. Select Notepad from the Drop-down list and viola!
Thanks for all the help guys. It certainly got me looking in the right direction.
I know this case has been solved, but it happened to me too and this is my solution:
1. Open regedit
2. Go to: HKEY_CLASSES_ROOT\.txt
3. Check the value of key: (Default). If it's empty, then the "New -> Text Document" menu won't show up.
4. The solution is just set the key value to: txtfile.