Well N45SF had this issues since it launched and Asus just ignore it. So we have to solve it ourself. Don worry, no money is needed, no risk of voiding warranty. What u need to do is, go to the following link

http://event.msi.com/vga/afterburner/download.htm

download the program call MSI afterburner. After downloading it, install it and run it.

U should see some bar on the left and some graph on the right. Look at the left, u should see three bars, core, shader and memory clock. By default, the core clock is 675Mhz. Ok, what u need to do now is, the core clock, u pull it down to 630Mhz, the shader clock will follow as u pull the core clock, coz its linked. Leave it, its ok, just let it link. Just pull the core clock down to 630Mhz(shader is about 1260Mhz) then u hit apply button down there. Then just go ahead and play any games u wan. Problem solved xD.

And remember, before u play any games, u need to use this MSI afterburner to underclock it first. Well for me, as soon as i open my computer, first thing is open this program and set the clock speed. So that i won't forget when i play games xD.

Cheers