Unable to get power supply replaced when under warranty

My power supply went out today, as a prior Dell Technician,  I unplugged everything, drained power from resistors by holding down power button.  Plugged the system back in still no power, tried the BIST still no power or light or fan. Checked warranty still good until April.  asked me 3-4x the same questions as if he didn't understand.  Then came the warranty he could see it was under warranty, but apparently since I purchased through Best Buy I had to transfer the warranty. Hmmm no! I needed to register but how do you register when your system does not power on.  Tried to xfer "invalid service tag" ... still no assistance.  What do I truly need to do in order to get my power supply replaced?