If you click on a link to a site collection and get this error :
And then go to the SharePoint Admin Centre and still see it in the list, but clicking the link still give the 404 error above :
Then is means that the Home Page has been deleted. To get it back, go to any other site collection, then Site Contents.
Copy all the text in yellow below once in Site Contents :
Go to the site collection where you get the 404 error and paste it to the end of the link after the site name :
The page will display in the Site Contents screen. Go to the Recycle Bin :
Tick the box next to Home and then Restore :
The site is restored :
Be careful when deleting pages from the Site Pages library – don’t delete the Home page or it causes the above issue.
Views from Veronique 
Nailed it! Great!
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This was very helpful to me,
Thank you
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Thank You very much!!
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Genio!
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Thanks for the help!
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He estado buscando esta solución por todos lados!!! Aprecio mucho su ayuda
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Thank you sssoooo much! You saved my life! I know that sounds dramatic but it was!!
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Odd indeed, I would log a call with Microsoft for that.
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Nice job — found and restored access to a page using this guidance. Thanks. 🙂
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What about when it shows the 404, but Home.aspx is still intact and not deleted. This is for SPO, specifically. Site was fine 2 days ago when the user last used it. All other pages on the SPO site work
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Pleasure babe.
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Pleasure.
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Thank you so much. Appreciate this
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Thank you so much Veronique 🙂
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Thank you.
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The blog is quite precise and informative.
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