ABS light

I have a 1992 Buick LeSabre, with 71,830 miles, the ABS light stays on, all brakes have been checked, and a new ABS computer has been installed. I am unable to clear the codes coming up on the computer when we hook it up to the car. The brakes work fine and the car runs like a top....any suggestions what might be keeping this ABS light activated??
I have exhausted all resources available to me......