00 ford explorer goes into gear but will not move

Hi, so my son used my 00 Ford Explorer v6
4x4 & from what I've been told he drove it
heavy footed about 20mtrs & slammed it
into park, then put it into drive reversed
fast & slammed it into drive -this went on a
few times (pains me to retell this story)
then there may have been a 'clunck' and
then the truck stayed on & reved but would
not click into gear & hasnt since. When
turning in on intially there are no noises its
normal, put into any gear it doesnt move,
just reves, then sometimes makes a grindy
noise when you try to put it into park again
& wont-but if you turn the truck off it goes
into park.

Any help before on this matter would be
much appreciated, this will come out of my
sons pocket & tho id love to let the local &
only trans guy build the bill-I know ill end
up forking out first & be drip feed the rest
hopefully before hes married & left home-if
its something we could fix (me supervise)
that would be great.

Thanks in advance