Dell had some bios issues with some models and PXE.
Update your bios.
I forgot to add that in my troubleshooting steps. It is now updated to the latest version of the BIOS. I get the same result. Thanks
Try removing 2 entries from your Pxe menu. Remember which ones so you can put them back.
Also if your entry for the D60 is long rename it to a shorter name, 12 characters or less.