If restarting does not work, it may be an issue with the power supply.
On the front of the Solo box, the network light appears to be 'on' but very feint. The power light is on full brightness.
I previously made the mistake of purchasing an entirely new Solo but the issue is the power supply from Slingbox are of poor quality. My second power supply crapped out yesterday and I just bought a new one on eBay from a different maker but specifically for the Solo. It now works again.