Yaesu's FT-100 is a low noise floor, wide dynamic range ham transceiver. The device is particularly well suited to DX'ing---long distance radio communications. You need to be an FCC (Federal Communications Commission) licensed amateur to transmit with this radio, though. Problems with the Yaesu FT-100 can include power, audio, scanning, receive and transmit issues. Fortunately, these can be corrected by following a few troubleshooting steps.
Turn the power supply on if the FT-100 won't turn on. If it is on, and you can't receive anything, verify that the "AF Gain" knob isn't turned fully counter-clockwise---turn it clockwise. Rotate the "SQL" knob all the way counter clockwise to reduce squelch. Make sure the external speaker jack, marked "Ext SP," doesn't have a redundant cable in it. It will cause the Yaesu's internal speaker to be bypassed.
Verify that an antenna is connected to the "Antenna" jack if you can't transmit anything. Look for a coaxial cable there. It's a good idea always to check this when starting the radio up, and before pressing the PTT (Push-to-Talk) switch, anyway, because damage can occur if you try to transmit and there's no antenna---the power has nowhere to go and ends up zapping the radio's circuitry. Verify that the label "TX" appears on the screen when you press the PTT button. If it's doesn't, check the microphone is plugged in. If the microphone isn't plugged in, no one will hear your transmission.
Close the "SQL" control on the Yaesu FT-100 if you want to scan and the radio won't. Turning the squelch knob too far clockwise will cause scan to stop on frequencies often and result in scanning failure.