I'm here to help you access your QuickBooks Online account. Let's get this sorted out.
Are you getting any error message when accessing your account? Any information you can add will be helpful for me to check for any related issue about it.
Meanwhile, do you happen to have a different email address that you might have used upon subscribing for your QuickBooks Online account? This could be one of the reasons why you are having challenges accessing your second account.
Next, let's make sure you have the correct website when signing into QBO. Please use this link: https://online.intuit.com/login. You can also try using a different browser.
On the other hand, you can reset the password or recover your user ID. Once done, you'll receive an email with a password reset link. As a reference, you can check out this article for further guidance: Reset your password or recover your user ID.