Hi Rick,
All storage on ESXi 5.0 and later is by default formatted with GUID Partition Table (GPT) instead of MBR...(to support >2TB datastores)
So for being able to successfully boot the ESXi server you need EFI/UEFI compatible BIOS.
Please check if the BIOS in ML570 G5 HP server is UEFI ready...?!
If not you can change the partition layout during ESXi installation process <Shift->O: Edit boot options>
After prompt to ENTER boot options type "runweasel formatwithmbr" then press Enter.
If this doesnt help follow this KB article:
VMware KB: Trending Issues: Installation problems with ESX/ESXi
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Regards,
P.