How to manually press a button?

So, I want arduino to remotely power up a Desktop machine (keeping CPU button pressed for 5 seconds and release)

Should I use an actuator for this purpose or some other kind of setup with servo motor would work as I need to physically press the power button on the CPU using Arduino?

I understand I need to use Wi-fi shield in order to control it remotely from my smartphone
Are there any other standard setups being used to physically press on a button?

Look into "Wake on LAN" which I think will do the job for you without complication.

Thanks, looked into "Wake on LAN" and it looks great!
But I would still want to know how to do it using mechanical way (as I dont have BIOS access on these machines and would also want to do it for the experience of it)