No sound on my dell optiplex 330

Unless you have headphones, you need speakers, preferrably amplified speakers.
Another way the address the issue is to use a cable to connect your computer to your home stereo if it has an auxilery input (aux/cd/tape input) then all you need is a cable with two male RCA plugs on one end and an 1/8 inch stereo plug on the other end.
The 1/8th inch plug goes into your computers' sound "out" and the rca's go into the aux/cd/dvd "IN" on the stereo.
this cable can be purchased for under 10 dollars at walmart, though amplied speakers wont be much more expensive.
Hope this helps you decide which direction to go..
Regards..