Recently the 800 MHz machine I had been running BOINC on died of old age. I have installed the latest version of BOINC on my new computer but all my credit for past work has disappeared.

How do I retrieve that information.

Not by making a new account...
So you will have to log in on the old account, the one you were crunching with. Go to this page and fill in the email address of the account. It must be another email address than the one on this account, as the email address is the unique identifier, meaning no two accounts can use the same email address.

A link will be sent to that email address for you to click on to log in with.
And then... well, change the password on that account to something you can remember and check if the computer you're now using is signed up under that account. I think it is as it sure isn't attached to the one you're writing with (no computers are).

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