Hold the DEL, ESC, F1, F2, F10, and/or Control key down during boot, it varies between machines. Most standard (home built or local shop custom) PCs will use DELete. HP/Compaq often uses F1, but those old Vectras used the Control key. Some laptops use some really odd combinations...
Navigate through the menus to where you can switch the AC97 Audio device on, or off if you are trying to run a real sound card, then exit and save the settings. Put the Recovery Disk in when the system requests drivers...