weird hardware problem!!

ok now this is really weird, my motherboard intel 865 GBF stopped working suddenly 1 day, it wudnt boot so i called my mechanic, he fixed it n left it at my place, when i tried to boot up the machine the same porblem came up, i called him up n he told me that he forgot to "short" the motherboard on button (watever that means) & told me to put a screw driver on the pins (9 pins on the extreme bottom right of my MOBO on a white plastic) I did that n it started working but then suddenly after a while i had the same problem but when i wud turn the cpu on the fan wud start n wudnt stop but there wasnt any display on the screen, so i called him up again, he told me to take the HDD connections out of the MOBO n start the pc , shut it & again put the connections back & start it again,n that worked
now my pc works for while then it either restarts or shuts down by itself n i have 2 do 1 of the 2 things that i ve mentioned 2 start it again... help me out with this!