Unless the bolts came out and starter is loose, (very unlikely).. the
starter needs replaced.  OR.. you have a couple teeth off the Ring gear of
the Torque converter flex plate.
If you're inclined, try to turn the engine a little with the belts/pulleys.

Usually though, that problem is intermittent for a while... bad luck for
you, if you can never get it to engage.

my guess is that the bendix (starter engagement solenoid that pushes starter
"into" the starter gear) has gone bad or needs cleening&light lubricating.

the worse scenario is that the starter gear is missing some cogs... , and it
accidentally stopped in the wrong place.
Try pushing the car a bit, while it is in a gear. If after that it still
doesn't engage, dismantle the starter and it's solenoid (bendix), and check
it thoroughly.

It sometimes happens, in cold weather, that a few attempts are needed before
the bendix manages to do it's job...