1. Make sure the network you're connecting to is 2.4 GHz, Loop does not support connecting to 5 GHz networks. Don't worry though, this won't have any impact on speed since photo sizes are far smaller than video streaming.
2. Loop does not support connecting to WiFi networks that have a web browser pop up or sign in page (these types of networks are sometimes found in public spaces like business Wi-Fi networks).
3. If the first two situations don't apply to you, sometimes a simple restart helps clear things up. Try restarting your Loop frame and your wireless router. To restart your frame just press and hold the power button on the back for 3 seconds then press it once more once the frame has turned off.
4. If you're still stuck and trying to setup Loop for the first time, try factory resetting your Loop. Tap anywhere on screen and hold for 3 seconds to display the service menu, then select the Factory reset option. This should clear up any issues between your frame and router.