you need to reinstall the drivers for your motherboard, in particular the USB drivers.
Likely the rear-panel audio port works, that is the motherboard's default and controlled by the audio drivers. However, the front panel is usually connected to the motherboard via a USB internal connector, hence the need to install those drivers.
If you don't have the disk, you can go online to the motherboard's manufacturer website and download all the needed drivers from there, save them on a disk or USB flash drive and install them.
Also, in case you have opened the PC case, make sure the internal USB connector between the front panel and the motherboard did not get dislodged.