If I am understanding you correctly, your system no longer boots, even with just the old RAM installed? IF that is the case, then you must have either caused some damage when you installed the memory, accidentally dislodged some component, or introduced a short somewhere in the system. Double check any and all connections that you might have dislodged when workign inside your system. Take anything else out that you added, and only have the factory RAM installed. If that solves, you can try to put the new RAM back in.
On the otherhand, if you mean that the system no longer boots with any combination that includes the new RAM, but fine otherwise, that means the RAM you selected is just not compatible with your system. The Aurora R7 motherboard is notorioulsy finicky with denser DIMMS. I always recommend suggest that folks use Crucial to purchase their RAM. They will guarantee comptibility, as opposed the trial and error of buying DIMMs form other sources. https://www.crucial.com/compatible-upgrade-for/alienware/aurora-r7