Sure, you can repair an ntdll that failed - there are many methods you can try; on the other hand, this is the easiest and most recommended one. It's a fact that unnecessary registry keys can interfere with the windows system and quite possibly the only way you can track down these keys is by using one of these utilities. To be on the safe side, it's a good idea to confirm the working order of the registry when doing regular maintenance such as backups - at least once a week. Nowadays, it's common for people to understand how their computers work, so they want to be able to troubleshoot their computers' various difficulties without having to call in outside help. It's important to pay attention to your system's upkeep - in the event that this care is lacking, don't be surprised to see miscellaneous errors and glitches.