Intermittent resets

My computer has been Intermittently turning off, i've tried to fix it by doing the following at different times:

-reinstalled windows and updated,
-ram and HDD's checks (windows)
-changed the CPU thermo glue multiple times,
-changed HDD config to raid array (occurred before array).
-changed the graphics card,
-cleaned all dust out of gpu/cpu/psu and motherboard,
-re ran cables and made sure there are no shorts,
-installed 'cool laboratory liquid ultra' thermo glue on my cpu heat sink,

Since doing the new thermo glue the last time the computer turns on, tries to boot, restarts then runs fine till it randomly resets; performance has also been slow running chrome with nothing else in the background.

I've no clue whats wrong or what to do now, would appreciate your help, i've checked/changed the power board and cable aswell.

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 7 Home Premium, Service Pack 1, 64 bit
Processor: Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz, Intel64 Family 6 Model 30 Stepping 5
Processor Count: 4
RAM: 2039 Mb
Graphics Card: NVIDIA GeForce GTX 560, 1024 Mb
Hard Drives: C: Total - 1907631 MB, Free - 1410402 MB;
Motherboard: Gigabyte Technology Co., Ltd., P55A-UD3
Antivirus: Microsoft Security Essentials, Updated and Enabled