First, it would be helpful if you provided the model of your Dell.
Can you explain what happens when you plug in your external drive? If you open My Computer, do you see a drive letter for the external drive? If you right click the drive and select Explore, do you see folders and files?
It says inspiron on the front, but I am plugging in an external drive into a laptop with win 7 on it and I don't have the laptop with me so I can't tell you the brand. I see all the folders on my dell, but on the laptop it only shows the ones that were put on it with the lap top. Not the ones that I put on it with my dell.
Go to Google or your favorite search engine, and do a search for "how to take ownership" for Win 7. That's the information you need.
Good luck with the new system!