My speakers still work but no sound comes from my pc

Here is the your audio driver
http://support.dell.com/support/downloads/download.aspx?c=us&cs=555&l=en&s=biz&releaseid=R94481&SystemID=DIM_CEL_3000&servicetag=&os=WW1&osl=en&deviceid=2430&devlib=0&typecnt=0&vercnt=3&catid=-1&impid=-1&formatcnt=1&libid=3&typeid=-1&dateid=-1&formatid=-1&fileid=122481

Check the following,

• Speakers, connecting cables and Sound Card are working fine by connecting to another computer.
• Speaker Cable is connected to an audio port (Audio/Video port in system box).
• Volume is MUTE / Low (in Volume Controller).
• Audio drivers have installed.

To Check follow the Steps:
• Go to Start>
• Control panel>
• Double click on "System" Icon> (it shows the System Properties Window)
• Select “Hardware” Tab>
• Select “Device Manager” Tab> (it shows the Device Manager Window)
• Select “Sound, video and game controllers”>
• Expand “+” symbol> (check the audio Codecs, Legacy Audio Drivers and others are not in Questioned Mark (?) symbol with yellow color. If there need to install the drivers ).

• If not, insert the motherboad CD, browse>select audio driver>install. After completion, restart computer and check.

Check for sound card is present( configured) on Op. System, normaly is sound card drivers problems, try to reinstall audio drivers