Colors of images change

Please check if there's a .lock file next to the LR catalog in the appropriate folder.

If  there's such a .lock file it must be deleted manually.

More informations about this, you'll find here: 

The Lightroom catalog cannot be opened because another application already has it opened - lrcat.lock (adobe.com)

so I restarted my computer 

You closed LrC first?

in the future, to find the best place to post your message, use the list here, https://community.adobe.com/

p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post (like this one has already been moved) if it helps you get responses.

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