How can I stop my laptop from humming?

Depends on where the humming comes from. Must be one of the moving parts. Does the machine vibrate or is it just a sound?

Maybe you can just stop the noise, by placing the laptop on a flat and even surface? If not…

If it’s the cooler fan, you shouldn’t stop the humming. It will stop by itself once the temperature inside your machine is Okay.

If it’s the hard disk, you should make a backup soon, because if the hard disk hums, it might break and you could lose data. If it is the CD/DVD drive, then take out any disk, clean the drive. (dry, with a soft paintbrush) and try again.

I would get a can of air and blow the heat sink and fan off, the humming is more than likely the fan vibrating because it as a uneven amount of dirt on it, plus if the heat sink is dirty, it makes cooling harder.