Open the AF control center and see if the words "Internal Clock" in the upper right corner are orange. If so, here's what to try. Click on the Settings wheel (also in the upper right corner). Now, in the "Clock Settings" dropdown menu, select "Internal Clock" (even if it is already selected). Note that sometimes you have to select it more than once. If it's working, you'll notice a brief spinning wheel followed by the words "Internal Clock" changing from orange back to white/grey. Basically, you're doing a soft reset within the software.
