Is there a method of remotely shutting down a PC using Crestron?

Install Eventghost on the pc. Then you can configure it to receive tcp or rs232 commands and have them trigger programming in eventghost. This could include shutting down the computer.

The trick is remotely turning it back on. Much easier to use sleep/wake than a full power off. Better still, let it sleep on time, then no need to send any commands at all.

You can send magic packets and use wake on lan to turn on most computers.

Yes, you can wake them, but not if they're completely powered off, usually.

I still think it's a bad idea to completely shut down.

the only time they won't wake, is if they had the power disconnected from them.  otherwise they wake every time for me.  You just have to make sure the Bios settings are set correctly.  it varies from motherboard to motherboard, but i haven't ran into a pc that I couldnt get to wake on lan in quite some time.

in the event that they do lose power, you can also set them to power on automatically when power is restored.  this is also a setting in the bios.