What I have done is removed the graphic card(560gtx) and installed an old one(xfx 9600gt), let's see if there are any errors/graphic card driver crashing.
I also have removed 2 RAMs and inserted them into other slots. Will soon test them with memtest.
If random restarts still persist(after checking rams with memtest with no errors) then either psu or mobo is the cause.
Thanks for replying again rolli59.