The bike is an older Trek 7000 with Shimano STX shifters. The problem is with the left (front) shifter. The derailleur shifts into the large chainring with no problem when I tug on the cable, but the indexed shifter won't click (or pull the cable enough) to move the chain to the large chainring. It clicks for positions 1 and 2, but not for 3. Also, the indicator that's supposed to show what gear you're in doesn't move.

Is this fixable? If so, how?

Thanks!