I think his .jar files are being associated with Winrar/saving as a .rar. He does have Winrar installed and I think by default Winrar associates a lot of files types to itself.
The client tool can fix this sometimes, other times .jar has to be unchecked in Winrars settings.
Deleted Winrar (not sure if uninstalled or an icon was deleted?) when I said not to :C. Doing so usuallyl keeps the .rar libraries or w/e and the associates, even though the program is gone.
The video below and the client repair tool might fix this. Winrar probably has to be installed again.
^Tool link.