problem regarding calendar download

I have a problem while using calendar module.I downloaded calendar module and saved it in xampp>>htdocs>>drupal>>sites>>all>>modules.I know that I have to enable it in administrator>>site building>>modules.there I have to click the checkbox.but my drupal is not enabling me to check that checkbox showing that some files are not missing.so I uninstall that module again.I did it again and again,but no progress.
Can any one help me.