I'd suggest you check the Samsung website.
I just did a random check and they had a pretty comprehensive troubleshooting guide with a step by step for no sound issues.
Since we don't know which model you have it makes it difficult to assist.
Here's the website link I was looking at http://www.samsung.com/us/consumer/tv-vide...agetype=subtype
It shows 3 models of 22" LCD TVs with PC connectivity. Their are various options in the TV menus to use other sound sources or disable the internal speakers all together. Once again depends on the model. I didn't notice a RCA Audio in for a PC except on one model, all had standard audio cable inputs for PC. Did see AV in with RCA plugs and know that that may not work as a audio source except when TV is set to Aux/VCR as the source. With a video playing via the PC you could try changing the source on the TV to aux and see if you hear sound.
Basics to check;
With headphones plugged into the same PC output jack do you hear sound?
It is possible that the headphone output isn't enough to drive the speakers in the monitor to a audible level.
Does LCD TV normally have any sound (such as in TV mode)?
Have the cables you're using been tested good?
Edited by Koinos, 05 December 2009 - 06:16 PM.