I have a gateway laptop, the cpu fan comes on for like 10 secs and goes off. I replaced it with a new fan and it does the same thing. Does it mean that the board is bad?

Sounds like you have a temp controlled fan. Its not hot enough for the fan to come on. I THINK if there are four pins, it is temp controlled. Does it ever come on after it goes off? ie, when the laptop is hot. Before posting try google. Backup. Use anti virus software.

Yep, all laptops have temp-controlled fans. It saves a bit of battery power. Sitting at the desktop, the fan will rarely even spin up, if at all. Fire up a game, and the fan will blast out all of the warm air at max. speed. Homebuilt projector: Samsung 1080p panel Pixelworks controller 2 HDMI, 2 Component, 1 VGA Homebuilt enclosure 120" 16:9 screen Connected to: HTPC w/ BD, satellite receiver, XB360.

The laptop is overheating and shutting down. What I found out that is weird is if I dont screw in the screws on the heatsink tightly,the fan will stay running but the computer still shuts off on its own. If the screws are screwed in tightly the fan will run for like 5 seconds and then shut off. The computer will overheat and shut off within 5 minutes.