"What if I did power on, but using only the generic account the seller provided?"
Do you know for a fact that the seller DID provide a "generic account"?
I realize that -- unless he told you so -- the only way to find out is to open it and power it up.
Did he in fact tell you this?
IF there is a generic account on it (which occupies the "501" space in accounts), you can get rid of it by doing the following:
1. Boot up and log into the generic account, which I think would be set up as an administrator.
2. IMMEDIATELY go to the users & groups preference pane, click the lock and enter the administrative password
3. Now, click on the "+" sign. We are going to create a NEW account that will occupy the "502" space.
4. MAKE SURE you give the new account administrative privileges. Give it a simple name and password (such as "temp" for both).
5. Once this is done, log OUT of the generic account and now log into the "temp" account.
6. Now GO BACK to users & groups and log in with the temp password.
7. Click on the generic account, and hit the "-" sign. We are going to DELETE it.
8. Don't archive it if the option is offered, just GET RID of it.
9. Now, the "501 space" is empty and ready for your ACTUAL account (which is on the backup drive).
10. Connect the backup and open migration assistant.
11. Give migration assistant time to digest everything (could be a few minutes).
12. I'd just leave everything checked and let the migration begin.
13. It will take some time.
14. When done, migration assistant should bring over your old account, and "drop it into" the empty "501 space". That's why we needed to create a temp account, and then delete the generic account which was occupying that space.
15. Now you can log out of the temp account, and log into your regular account. Look around to be sure things are right.
You can now either delete the temp account, or leave it around. I'd leave it around -- it takes up no space, and you never know when you might need to use it again.
