My laptop's fan often works fine when the laptop isn't heated. But when i indulge it in some heavy activity and when it starts to get heat up. The fan stops automatically even though when the fan stops the laptop isn't heated that much. When the fan stops the laptop shutdown due to over heating. And when i instantly restart it the laptop fan never starts from the boot up not until the laptop cools down .but often it won't start until i leave it for a hour. Whenever the fan works fine there shall come a point when the fan would stop working. sometime the period extends to half hour and some time even 3 hours if I'm just browsing and stuff. I took it to repair shop and got the fan cleaned and serviced but the problem sustains. The person told me it has sensor whenever it shuts down the fan the fan would resume start spinning when necessary. Sometimes this happens but most of the time it doesn't. The fan is absolutely fine, i got it tested. I think it has something to do with the sensor or built in settings. I cannot afford another laptop. I need a simple software or settings solution. Maybe a way i could restart the fan whenever it stops. And yeah the fan varies in speed according to laptop need but as i told it would stop after some point. Help!!!!!

Once in a while a poor soul has a failed motherboard. It's not drivers or settings as they have already reloaded OSes and drivers. There's a last hurrah hardware fix which is to rewire the fan to a power source. I usually pick up some USB +5V (avoid fast charge USB ports which can crank up the voltage) and the fan will then run as a mid range speed every unchanging. If that's not speedy enough you pick up some switched voltage in the power control area (too advanced for most techs and there is no documentation for this so your electronics background is called into play.)

The OS is windows 7 ultimate. And as i mentioned the fan works fine. Often i don't face this issue but when i overwork it the fan would stop ultimately killing laptop. I would really like a software solution rather than hardware. As i also mentioned i took the laptop for inspection and found everything works fine.

rproffitt I'm not a tech person i don't even know to open the laptop in the first place.Although i know my way around windows and softwares. As I'm mentioning it again. The fan works for a simple use but gives up sometimes mostly when i do some heavy processing stuff like gaming or just multitasking. The fan works fine in 4/10 times of usage. But i cannot work on it because there is always a chance of it shutting down. It seems to me something of a sensor problem or software

So it's Windows 7 and "Ultimate." Good to know when discussing such things as it matters.

You know that the fan is fine but you don't know if the sensors and PWM control system is fine or not. Since it looks like the OS is not stock you should at the very least install the drivers for this PC from its maker. I find folk ignore that all too often.

From https://www.acer.com/ac/en/US/content/support-product/3279;-;Aspire+5742Z at least the Chipset Driver which is where the fan control should live.

If that fails then you can try fan control software and see if you can set the speed manually. There are many for Windows 7 so I will not pick for you. If this fails then it is hardware and the hardwire method could avoid replacing the motherboard.