Hello adriansam and welcome to Seven Forums.
You could try a Repair Install. Otherwise you'd have to try to backup all existing files, documents, photos, etc because a clean install will wipe everything off the hard drive.
Repair Install
It's also possible that your Lenovo has a hidden recovery partition that would let you return your machine to factory specs (just like the day you bought it.) But again, you'd lose all of your personal data.