loss of audio

since reformatting i have lost sound to speakers, though i can hear thro headphones. i have lost the volume control and also the horn on tray desk and it appears that the integrated sound card is not installed, i have tried reinstalling the drivers from the mb driver disk and the audio file from windows to no avail, the mb is a m748lmrt windows 98 p111 156 ram if i install a new sound card , i believe the on board modem will not work?? grateful for any help thankyou
ralph