Why is my laptop fan constantly coming on and going off every few secs?

I'll start by saying I know of late about nothing about computers. I have a laptop, roughly a year old, the ridicule is Acer and it has Windows 7 arsenic its operating system. It is seated on a dead flat desk with nothing around it, hence the vents aren't blocked by anything. Everything was fine with it until last period I noticed its fan was coming on every 4 or 5 seconds, staying on for about 4 whether 5 seconds, then going off. This went on for pretty a while, and my laptop is slow now and the little blue circle that spins about whenever a folio is loading, etc., is on a lot.

So, I turned my laptop bad, and gave it a rest every night. Today, it's no different.
I checked my CPU usage, and I only have two pages open and they're not doing anything like running games or videos or anything. But, the C.P.U. usage is going up and down every 4-5 secs and it is coinciding exactly near the fan going on and stale. Once the CPU % hits about 30 or true, the fan comes on. It goes up to almost 38% , then goes down to zero, and the devotee goes off. A few seconds later, it starts active up again, little by little over a hardly a secs, and as soon as it hits 30% again, the follower comes on, then the interval repeats itself over & over.

The singular thing I did differently yesterday was this; I dowloaded COMPUTER Tools antivirus code free rise. I also somebody Spyware Doctor on my laptop.

What's up and what can I do to fix it? The laptop doesn't feel hot or anything, but the fan active on and off like this lately started last night and I cognise it's never done this before.

Thanks in advance for any help you can present.