I want to ensure this is taken care of. First, may I know the error message you've received? Any information could help us determine the cause of the issue.
On the other hand, you can try checking your bank's website to see if there are issues on your bank's end. You can look for any display problems as you navigate the website. These can block QuickBooks from linking to your bank.
If everything's fine, let's access your account using a different or private window. Sometimes, the browser is full of frequently accessed page resources, which causes some errors or unusual responses.