Windows Store

[Barry]

Hello, I have set up my Microsoft Account OK after many tries and I can now use Cortana OK.
I went to the Store to download an App for Gmail.
I was asked to re-enter my password, but it shows an old email address, not the one I am logged into for my Microsoft Account.
I have tried using my present password but the Store rejects it :-(

Any thought please on how I can fix this?
Barry