Can I downgrade back to windows 7 when the start menu isn't working?

[Windows Central Question]

I have the Critical Error message in Windows 10 and would prefer to return to Windows 7. I just watched a video on You Tube of how to do this but since I can't access the start menu how do I get to the 'settings' etc?
Thanks

 

[Jazmac]

Look on the tray on the lower right side for a icon that looks like a business card.

 

[Vee Crowther]

Thanks but there is nothing on the tray. The big Critical Error message is blotting every thing else out. I am posting this on my other computer, otherwise I would be really stuck.