sharepoint website access denied to certain users

I modified the permission list on the sharepoint homepage by deleting most of the users. Then, I re-entered the same users back on. However, the user who had the sharepoint web browser closed at the time could no longer access the website. The ones who had the web browser opened still can use it. It seems like it has to do with user being authenticated or not, but i don’t know how I fix it because the permission list looks correct.