Does the network light blink or is it just off? If it is off then is seems like it could be a PS issue. If it is blinking then it might be something else. Just last night I was installing a new Slingbox and I could not get the network to function. It turns out that I needed to reboot my router because the DHCP server had stopped working. After the router reboot the Slingbox popped to life.
Before you try a different power supply, I recommend that you take a look at these links;