If you have a problem with installation or activation of any plugin probably it is because your server interrupted installation of it. This kind of problem can happen if your server have very low limits related to connection e.g. time limit. Please delete broken folder and install problematic plugin again.
1. Install File Manager
2. Visit /wp-content/plugins/ folder
3. Delete problematic folder:
|Plugin Name||Folder name|
|Contact Form 7||contact-form-7|
|MC4WP: Mailchimp for WordPress||mailchimp -for-wp|
4. Install plugin again