For problems with sound:

Verify that the TV or audio system is not muted.
Check the settings of your audio output device to make sure it "sees" the PS3. Also, verify that you are using the correct audio cables and that they are properly connected.
When playing audio discs, verify that the music you are trying to play is not copy-protected. Certain copy-protected discs may not play.
Verify that your system's audio input and output settings are set up correctly.

For problems with video:

Verify that the input mode on your TV is compatible with the connectors used by the PS3.
Your PS3 video settings may have compatibility issues with your video output. To reset the PS3 to standard video, disconnect all components and hold down the power button for five seconds.
Ensure that the video definition is the same for both the TV and the PS3. When using a HDTV, the PS3 must be properly set up or the image will be distorted.