I have an AMD64 machine that I loaned to a friend for a couple of weeks and when they returned it, it wouldn't start at all.
I took the cover off and noticed that when you plug in the power cord with power that the CPU fan turns about a half turn and that is all that takes place.
I have checked the power to the motherboard and am receiving 5.5 volts from the power source but nothing is happening anywhere else.
I'm thinking the motherboard is fried but I dont see any signs of anything being hot etc.

I have built my own machines but have been out of the loop for a couple of years now.

Any ideas on what I should check next?

Try unlplugging the cpu fan for the processor and dust it then unplug the power cord connecting the motherboard then reconnect them

Thanks, I just tried that and still doing the same thing.

Desktops in transit tend to loosen connections with memory sticks and PCI/AGP cards. Try reseating them. I've seen with my own eyes AGP card completely unplugged after 10 minute ride, and the screw on the card was tightened.
Also check motherboard's power cables if they are loose.

Is the CPU picking up the heat when turned on? If so, you might have fried CPU on your hands due to dead CPU fan.
Next suspect would be PSU.

Any info from your friends?

What about the processor itself have you seen any defects funny smell and also the processor jack is dusted fully? Have you tried to reset the BIOS of the motherboard