How have you connected the audio cables to the TV? The 3250HD has component, DVI, and composite video out. There is also two analog audio outputs (for the component and composite video) and a digital audio output. Make sure that you are using a TV and not a monitor. Many monitors do not have built-in speakers. (In that case, use external speakers.)
If you use the digital audio output, make sure that your audio receiver audio input is connected to the set top box audio out. Then make sure to set the correct source for that audio signal. (Note the TV may have a digital audio port; that is an audio out.)
If you are using one of the analog audio outputs directly to the TV, make sure that you are using the correct set of audio IN on the TV and audio out on the set top box. (If you are on the Component input, your audio won't be heard if you are using the Composite audio output.)
Next try different audio cables. Make sure that the TV speakers are on. (Some TVs have an option to disable the speakers if you use external speakers at times.) Try connecting the audio output to a receiver and speaker system (or speakers with aux in). You might need an RCA F/F to 3.5 mm M adapter for some devices. If another set of speakers do not work, then the set-top box probably has a broken audio output. If another set of speakers work, then the problem is with the TV audio. This could be a problem with the jack or the speakers.
I hope this helps.