Many users experience configuration problems with sound that can be fixed with KMix. Right click the speaker icon if it is present in the lower right and select "show mixer window". Once you are there you may only see a single mixer. Just click "mixer" at the bottom of it and it will open another window, possibly with more mixers. If you do not see one called "speaker", click settings>configure channels. You may have to select speaker from the left side group under "available channels" and drag and drop it to the right side under "visible channels". Once done, just close that window and adjust the master and speaker sliders until you reach your desired sound levels.
If you already see the speaker in your mixer, make sure speaker or master are not muted or set too low. Adjust to your desired levels.
If it's beyond those, post more information about your configuration and problem and I'm sure more help will come quickly.