XPS 400 Upgrade

Recently I purchased from you a 1TB 2.5 inch SATA (7,200 RPM) Hard Drive (Kit) with 2 Corsair 2 GB (2 x 1 GB) 240-pin Replacement DIMM DDR II Memory Module.

Prior to my purchase I asked my sales rep if I could run a 64bit OS with this new upgrade. The answer I got was YES!!!

I had already purchased a copy of Windows 7 32bit so since it was unopened I sent it back and purchased a 64bit OS.

Today I installed my new hard drive, ran Windows 7 64bit and guess what? I doesn't work. It says my CPU will not handle a 64bit OS. Oh, wonderful. So now I'm stuck with an OS that I paid $145 for and I can't return it.

I also have the correspondence from this Dell service rep where he states that, Yes, I can run a 64bit OS.

I called Dell and got no where. So what am I suppose to do now?