Yes C1 Pro can be activated 3 times. Did you install it and then have a problem and change hard drive or motherboard or something which the software might identify as a new device?
In any case, just launch C1, and click on Help > License Information and you can see your activations
To change things go to phaseone.com, click on My Pages, login to your account and then click on license management where you can activate and deactivate what you need to. It'S PROBABLY BEST TO JUST DEACTIVATE EVERYTHINg and then just reactivate them on your three installation computers.
Sorry about the all caps...