Gateway MT3104b Turn Off randomly

Dear all.
My laptop has been drive me crazy. i'm not sure what to do with my laptop and end up i bought a new laptop recently. But, i won't give up on try to repair my laptop and i will use this laptop as a toy for me to play. i will try everything possible to repair this laptop even if i need to change component on a motherboard.
I read through the forum and tried all the possible solutions available through this forum.
First time when it turn off itself is due to the temperature it too hot and the fan blast at full speed. Before it turn off i might did silly or stupid thing. I put my laptop on top of the wet cloth. just try to reduce the temperature . Then, what happen later it turn off itself. i try a few time to turn back it on again but it take a while. in fact i have to let it be alone for a few minutes before i can be possibly to turn back on again.

1. By read through this forum, i found that this was a normal issues regard to thermal issues. So, i open my laptop, untight the screws that attach to the processor and give it a clean on the grill that cover from the hot air ventalition. I fit it back on again and seems like the problem is still there.

2. I wonder the issues is because of i fitted the heat sink using thermal compound instead using thermal pad which is that come with it. I remove the thermal pad and guessing that the normal thermal compound will do the job. so this is still a question mark here. But when i fitted with thermal compound, i turn my laptop on and let it run through and i monitor the temperature constantly. the result shows it run at normal temperature which is at 40-50 degree celcius. But still, it turn off randomly. sometimes take a day to random turn off. sometimes it take a few hours or minutes. sometimes it won't turn on at all. u can hear the hard disk turn off after u press switch On button.

3. I might think that there is a problem with the fan and i took the fan out and test it by my self by applying 5v to the fan. the fan work well. The fan got 3 wires. red, black and yellow. i assumed that red is 5v, black is ground (0v) and the question is what is yellow colour for? the fan use brushless dc motor.

4. so the issues here is no longer temperature. since, when i monitor the temperature. it always running at normal temperature. I confirmed this by compare it to my other laptop. it around 40-50deg. How do we know when the fan should turn on?

5. What else do you guys think that might be a problem. The battery is ok. power from ac also ok. in fact i also did change a new processor. definitely i'm using same model processor. but still no joy.

Please guys.. share you info...

thanks