You should have saved the old "key" file.
In fact, it's a plain ASCII text file with -guess- the key number, so you could have got it from there. Simply replacing/inserting the old file would work, too.
Looks like you deleted it when re-installing, too bad
Better either go searching for the manual or pepare for spending some more bucks for a 2nd Version of DOM2
And if you find the manual, note the key number on the CD. Without the CD, you wouldn't be able to install anyway.
And back up the complete DOM2-folder to CD-R next time ..