My sound isn't working on my XP computer! Please help!?

So basically, I reformatted an old office computer we had, which is running XP Professional. I went to plug in a set of speakers, and nothing happened, no sound. There is not even a volume icon in the system tray because it is not reading a sound device. I checked the device manager, everything seems to be ok (drivers are ok, no alerts/exclamation points). So the device manager says everything is working properly. I even went into the BIOS and disabled, booted, rebooted, enabled the onboard audio, still nothing. The sound jack is part of the motherboard. When I go to control panel and then sound, it reads it as if there is no sound device. I know the speakers work because I used them in another computer, and I know the driver works because I used the same driver that it was already running prior to reformatting. I would also say it's a bad sound port, but this computer has jacks on the back and front, and neither work. Can anyone help? Thank you!!