Sounds like a problem with the Blade Brake Clutch (BBC) underneath the engine. If you got 24 years out of the original one, you may have set a new record! There is plenty of information on the web regarding BBC issues on your mower that you can search for on this and other mower forums (see post above as well).
You can: 1) replace the entire BBC, 2) possibly repair it (usually the bearing dries out and then siezes up, which it sounds like yours has), or 3) convert the mower to a non-BBC setup (remove BBC entirely and install a conventional blade adapter and blade from a non-BBC, zone-start Deere mower - your mower model without the BBC would have been 14SZ, with the 'Z' standing for 'zone start').