My computer reboots when I tell it to shutdown

"I asked the IT guys to try removing the PCI/PCIE cards that were installed to see if they were affecting the shutdown process.

Sure enough, removing a Moschip Semiconductor serial/parallel port PCIE device resolved the problem."

It's perfectly possible that there's a hardware or firmware flaw. Flashing the BIOS might help. If not, you could actually install Windows (or borrow someone's hard disk running Windows, since these computers have the same hardware) and see if Windows can shut it down.