There are a couple of WWV signals, and depending on conditions, you might not receive all of them. If the 710 is programmed as the factory set it up, channels 13 through 20 are time signals. The first 5 are WWV, the last 3 are CHU from Canada. Usually channel 15 and 16 (10 and 15 MHz) seem to have the strongest signal.
The 710 is also set up for auto tune, so it should tune up when you key. You can try it manually by selecting a working channel like 4A (#77) and hit the tune button. You should see your ammeter move by about 10 amps. Then try saying FOURRRRRRR into the mic. The radio won't transmit without input from the mic. The ammeter should move a lot and the bar graph on the front should go almost all the way. Also, when using the mic, most of the ICOM mics need to be driven by getting your lips right up on the mic.