Was the PC you were running setup on a wireless device or was it connected to the router via Ethernet? A Slingbox M1, can in fact, only be set up from a device that can search for wireless access points by itself. This is actually explained in this article I have linked below:
If you can't get it through the normal wireless means, you could always try a WPS setup (if your router supports WPS), here is some more information on WPS setup:
And of course, if you still cannot get it on the wifi; run the Slingbox through a hard reset:
Hope this helps!
Sling Media Forum Moderation Team