1. First of all, you need to reset the username and password for your google account.
2. Go to the browser settings, here you need to clear the cookies and cache data. also, you need to update the browsing data.
3. When Gmail account is not working, you need to check the account settings. also, make sure that the gmail servers are working perfectly fine.
4. sometimes, Gmail users are unable to access the account because of the server issues. so you need to check the server details. make sure that the server is working fine.
In case, if you need more help, you can visit: what to do If I can't access my Gmail account
