Trying to install OpenElec

I am trying to install Open Elec on to a Dell Precision T7400. I went to OpenElec and downloaded Open Elec Generic X86 64-6.03. I extracted the file and wrote the file to the same USB drive. I changed the boot order to USB and put the USB in the drive in the machine and powered it on. It tells me there is no bootable device. I am not sure how to tell if it is the computer or if it is the USB drive. Any ideas? I am wanting to load MythTv or other PVR and create a large storage volume on this machine with Free NAS.

I tried to create a user on the OpenElec forum but their Catchpa does not show any way to complete it.

Thanks

John