Have you disabled onboard sound from the bios?
When you turn the computer On, hold down the DEL key on the keybord, this will allow you to enter the bios setup. Look in your manual, for further instructions.
If problem persists, disconnect the power cable, open up your case and take the sound card out. (touch some piece of metal before, before touching components).
Put the power cable back on. Turn the system on.
Download Driver Sweeper and install it http://www.guru3d.com/category/driversweeper/ . Once installed, run it and remove all creative drivers.
Switch off your system, disconnect the power cable and put the sound card back in to a different PCI slot, not the same one that was in.
Put the power cable back on. Connect your speaker cable to the green socket. Turn the system on.
See if windows detect the sound card, check if it’s installed correctly from Device Manager (control panel).
Any sound?
If not then Run Windows update, select check for updates , then click on Optional updates are avialable. Is there creative sound card on list, if yes tick it and click OK? This might take several minutes, once installed restart your system.
Any sound?
If not then go to creative website and download windows 7 drivers from there. Run the setup files, and follow the screen instructions.
http://support.creative.com/Products/Products.aspx?catid=1
Do restart your system.
Any sound?