Thinking back, I believe I actually had the exact same problem -- at least, the Kindle was stuck in the Store and couldn't find its way out, even when pressing Home. Other than that, it looked perfectly normal...
A reboot fixed it for me too. Note that rebooting means holding the power down for ~20 seconds. Simply clicking the power button (even for ~6-7 seconds) is simply putting it in sleep mode, even if the screensaver doesn't pop up.