No sound after installing window XP - Dell Dimension 4600 PC Desktop

Sounds like a driver problem. Sound drivers dont get installed by default on a lot of systems
If you find your dell service tag, on the back of your computer.
best to write that number down.
then you go to dell's site,
http://support.dell.com/support/downloads/index.aspx?c=ca&cs=cadhs1&l=en&s=dhs&~ck=GuidedPathHomePage and find the service tag on the back of your system. Click on the first link  "choose by service tag".
enter the number into the that will bring up drivers pertinent to your system. if more than 1 driver for audio is displayed, you can lookup the original system configuration at the dell site as well. in the left hand column under "Product Support" and 3rd line down, "system configuration". This section wont help you if you have an addin card installed that isnt original.
download the file.
run the file. 

You never know ur speakers could be blown or you put it in the wrong input it's usually the lime green one