Most often the linkage between the wiper motor and the blades has either come apart or broken. Many vehicles have access to this area under the hood, closest to the firewall. The linkage can be purposefully "break-away" type if you try to operate, or "man-handle" wipers frozen to the windshield.
RepairPal Certified shops can diagnose and repair your 1991 Chevrolet Cavalier. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.