G:\$Mft is damaged and unreadable . Execut CHKSK

Hello ,

French with poor english, I'll try my best to be understood: :huh:

Evry time since 3 days when I use CCleaner without disconnecting my extern hardrive,

I get this message out of the tool bar on the desk:

"The file G:\$Mft damaged aud unreadable.

Execut CHKDSK"

(in french :

"Le fichier ou le repertoir G:\$Mft est endommag? et illisible.

Ex?cutez l'utilitaire CHDSK")

What is wrong with my computer?

What should I do ?

Thank you for help.

eriq