Shifter - Park issue. Where do I look?

When I left work everything was fine. When I got home, I could not put the truck into Park. THe shifter would seem to move to the park location but the indicator light would blink out and I would have to use the hand brake to keep from rolling backward. The engine would not start unless I shifted to neutral.
The key was also removable in this so called Park position.

Right now I am using the truck with the hand brake but need to fix it before it locks up (It has given an indication of locking the shift lever but a little finese has gotton thru it)

SO where do I look? Steering column or transmission linkages?

I swear this truck knows exactly when money is tight and breaks accordingly.

96 Chevy s10 4X4, 6 cylinder, 200000 miles

Have a look at the shift lever cable and linkage.
Automatic transmission look at the lever and cable on the side.
MT