happened to me as well after a power outage. Did a factory reset, and all is well.
except i had to re-link the roku account again.
currently it's saying "synchronizing with account", so hopefully i don't have to re-link all my channel store services!
(update) -- no. looks like i have to re-link my services. ugh.
When you do a hard (factory) reset, it returns the box to factory conditions, so you start over and link everything from scratch. Unplugging the box or momentarily pushing the reset button does a soft reset and reboots the box, and retains all your settings and links. Do a soft reset first. If that doesn't help, then do a factory reset.