Fan trouble with my Acer

Hello /rtechsupport! My laptop an Acer 5749z running windows 7 that i bought a year ago is having trouble with over heating, its fan wont turn on and if i do anything other then lightly browsing the web it heats up quick and shuts down.

IF the fan is running it runs perfectly, but it seems to turn on at complete random and so i have to just leave it on until i hear the fan start up! If i want to watch a youtube video or do any gaming. It could be the instant i open a Chrome tab or not at all.

So my question is, is there anyway to get my fan running when i need it (gaming, video, photoshop)? i have speed fan installed but it doesn't seem compatible with my motherboard and will only tell me my temps. I've also opened it up and cleaned the little dust that was inside the fan and around the heatsink.

Thanks for any assistance you can give!