I went into the BIOS and changed the boot order to show the OS drive first (it had been third), and disabled booting from any other drive besides the OS drive and the DVD drive. I then booted into Windows, and added the 2TB drive. Once again it was recognized and assigned a drive letter--seemed normal. Then I shut down the computer and started it fresh, with the 2TB drive still connected. It froze on the initial Dell splash screen, and also didn't light up one of my other external drives. (I have 5 1TB drives besides this one, and normally when I boot, all 5 of them have little lights that light up. One of them didn't this time.) So, bottom line, I guess it didn't end up helping to change those BIOS settings--even though it sure seems like it should have, if it's now not even supposed to be checking the drivers
of any of my external drives.