System shutdown when playing big games on A.C power supply

my system specifications are given below:-

System Manufacturer--Acer
System Model--Aspire 5755G
Processor--Intel(R) Core(TM) i3-2330M CPU @ 2.20GHz, 2200 Mhz, 2 Core(s), 4 Logical Processor(s)
OS Name--Microsoft Windows 7 Ultimate 64 bit
Installed Physical Memory (RAM)--4.00 GB
graphics--nVIDIA GFORCE GT 540M CUDA 1Gb
directX version--DirectX 10

my system shutdown when playing big games like Max payne 3, Battlefield 3, call of duty modern warfare 2, etc on A.C power supply.
when i played these games on battery power of my laptop it works fine.

i recorded my nVIDIA gpu temperature on A.C power supply when playing a big game goes to 70-80 'C and max goes to 96'C.
and when i am not playing game and using my computer for general purpose it's range between 55-60'C.

plz help me.
what should i do?????