Will not shift when running, will shift when off. on 2000 Isuzu Hombre

The truck was shifting without problem and then started getting difficult to get it into gear until now and I cannot shift at all. When I turn the engine off, it shifts no problem. What could this be?

sounds like you have a clutch failure. get a shop to verify and give you a bid.

Isn't it possible it needs a clutch cable or gear grease? We do our own repairs usually and we're hoping its something we can fix. So, if you have any other ideas, we're all ears.