Hello,
Your downloads are within your account on your downloads page.
Just login to your account, there is also a link within your email with your purchase information.
Click on the downloads - either the large square or the link on the right column
You should find your download there. If you copy your key, and go to the admin page on your cart. Extenssion > Install Extension . Select the Network install, paste your key in the field, it will neatly install for you.
If you have done this and there is a different problem - just post again.
Lee