95 lumina won't shift

Hi all...I know nothing about cars so please bear with me. My car won't shift into gear. I managed to get it into reverse but that was only after sitting there idling for a few minutes. It still won't shift into any other gear and I did make sure the fluid is full. What could be the problem?

Do you mean the shifter won't move or the trans is in gear and will not move?

The shift knob moves just fine. The tranny won't go into gear.

If it is full of fluid, I suspect the trans is bad.