You're best bet is to use Impulse. Assuming your games are registered, you should only need to install Impulse, input your e-mail address (the one your games are tied to) and password, and then download at your convience. You need never use Impulse again thereafter.
Your games could have been registered by buying them from the stardock store (since you mentioned e-mail and activation serial #, this might be what happened). Alternatively you could have registered them manually using either "Stardock Central" (now phased out), or "Impulse".
If that doesn't work, go here and try the download Impulse button.
If you are using Impulse, and can't find your games, you may need to contact sales at stardock.
I can't think of anything else you can do beyond what I mentioned. Good luck.