Hi gmpy1, I think you purchased a SATA drive instead of an IDE one.
What is the model number of your Dell?
There are two possible options:
1. Keep the SATA drive & get an PCI SATA card, e.g. click here.
You might also require the correct power cable adapter, e.g. click here
2. Return the SATA drive & get an IDE drive, e.g. click here