Migration Assistant wont see time machine back up

[gobes]

Hello,

Had to have some repairs on my macbook pro, new logic board and hdd - so I need to restore the mac to the time machine back up I have.
They gave the mac back with 10.6 installed, so I've upgraded it back to 10.7.

But when I use migration assistant, it won't show my back up. But it will show the back up of another mac backed up to the same drive. So I'm really struggling to get any of my back up recovered and am getting a bit worried...

Have searched but have found nothing that's helped. Sorry if i missed anything.

Any other ideas on how to get the back up loaded? Thanks for your help.

 

[gobes]

I've got it to show it in recovery mode, but when it then loads it, it says:

"The backup cannot be opened.
If this is a password-protected backup, you entered an incorrect password. Otherwise the backup may be damaged."

I know i entered the correct password.
How can I check if the backup is damaged?