Hi, I'm Sandy and I look forward to help you today.
I'm sorry about the issue.
Please click the link: https://gmail.com
Please tell me the outcome at the box given below.
If it shows you logged into another account, please sign out of your new account and try to login into original(different account).
Click the link: http://mail.google.com/?logout
And then try to sign into your original account: http://gmail.com
If this does not resolve the issue, please let me know.
And if you can take a second to rate my service(-OK or more -by clicking stars at the top of the page and choose submit), that would be greatly appreciated.