RCA Model 27F520T - it has no sound everything else is perfect?

I'm not sure what options are available in your audio menu, but here are some things to check before having a repairman check:
Click on menu screen, then select audio menu.
If there is choice of external or internal speakers, select internal.
If there is a noise cancelling option, deselect this.
If you are using remote to increase volume, try the manual volume button on tv.
Does the volume bar at the bottom of the tv increase as you adjust volume ?
Hope this helps