Hi Vincent,
Is there a lot of light getting in through the top/side? these decks have
optic sensors and can be tripped into doing strange modes with light
otherwise sounds like a faulty switch contact or something similar.
when you say play button do you mean on the set or the remote.
~Its possible the remote if someting was spilt into it may do that.
if its not related to the remote then there may be a faulty switch on the
front panel. its certainly not a common problem.
I presume you've unplugged and plugged in again to reset the machine!

Other possible causes, dirty mode switch contacts, or poss a capstan
motor control fault , but that would be very rare. its more likely to be one
of the above.

hope this helps
AW