I had an external drive that caused that problem with a gigabyte board.
I just left the drive disconnected until I needed it, and boot times came back to normal.
You could do that but it's a real pain in the a** and it's a brand new computer. You shouldn't be having that kind of a problem with a brand new OEM computer and it's an unnessary hassle. I agree with das that it sounds like a HDD problem and as he said I would call Dell. The problem is you're going to be talking to some dumb monkey over in India that has horrible tech support.