Weird Autopilot disconnect logic and no Autothrottle response.

[swap17]

So, did a 4.5 hr flight from Egypt to Denmark on the MD-82, everything went fine until the last 30 mins of the flight, My Autothrottle stops responding to Speed or Mach settings, even on disconnection, it does'nt budge from it's original position when given manual Joystick inputs, and when you disconnect the A/P using the assigned button on the Joystick, neither does the flight control respond. the FMA simply indicates VNAV LVL and AT OFF, which is a bit conflicting for a beginner like me. So, is there something I am doing wrong? Anything that I missed, or is there a methodology to disconnect A/T and A/P. 

Thanks,

Swapnil.