So I have a single ESXi 5.1 host that I have 2 VMs on. A Windows 8 PC and 2012 Server. The Windows 8 PC was running great. But all of a sudden it will suspend itself and the only way to get it back is to power off and then power back on.
Does anyone know what might cause it to automatically suspend or if there is something I can do to stop it?
This is most likely the (Desktop) GuestOS Windows 8 entering standby mode as a "power saving" measure. Check the power policy settings on the guest and disable standby/hibernate mode.
You can also tell ESXi how it's supposed to handle guests that try to enter standby mode. The default is to suspend the VM like in your case: