Hi there, blackmunhauling.
When you have QuicBooks Desktop (QBDT), it doesn't mean that your account in QuickBooks Online (QBO) is syncronized with it. Although you can import your transactions from QBDT.
As of now, you can try check if you have entered the correct email address or username. Also, you if you are referring to QuickBooks Self-Employed, you have to use a different link to QBO.
Please check this link to know the correct log in page of the product you are going to use: https://quickbooks.intuit.com/login/.
If you are referring to something else, additional information would be helpful. I'm always a few clicks away. Take care.