Whenever you cannot sign into the Google account. it means, something is wrong with the user account or password. Here are the gide to fix the problems.
First of all, you need to reset the Gmail password.
Check that the Gmail servers are working fine.
Let's go to the Gmail settings and check the IMAP and pop3 server settings.
Sometimes, Gmail is not working because of the browser or mail application issue. so you need to reset them. after that, you should try to access the Gmail account once again.