|I will second the suggestion put forward by lurkswithin.|
I note that your PC is a Dell. Therefore it will most likely be an SLP (System Locked Pre-Installation) BIOS locked PC.
When sliptreaming you will also need to pay attention to your OEMBIOS files as they will allow you to preserve your SLP status and thus not require any activation post install.
Here is one example that shows how it can be done:
☺ When everything else fails, read the instructions.