Here is tough one for you guys,

Sony WM-F15. Replaced almost everything except the motor and main board. So any ideas would be much appreciated. So press play it starts to play then stops, Just like the tape has finished playing, Play button pops up. 

Any ideas would be great.

Also fast forward works and rewind works fine

My machine had same problem. I cleaned "pinch roller" and "pinch lever" using alcohol. They had stuck each other. Therefore "pinch lever" isn't pushing down "playing head" while "pinch roller" is revolving.
Good luck!
http://www.freeservicemanuals....wmanual/Sony/WM-F15/