Reinstalling CKEditor module
Disable the Module
Uninstall the Module
Delete the Module folder from sites/all/modules
Remove the CkEditor folder from site/all/libraries
Clear the Cache
Copy the CkEditor Module to site/all/modules folder
Copy the Downloaded CkEditor to sites/all/libraries folder
If in *nix systems, check the folder permissions. (Most of the time this happens to be the issue)
Enable the Module as usual. 


More info is given CkEditor docs