OK, since you are new to the computer world, then here are some tips.
If you have a recurring issue, you should be making notes of some type as to what 8exactly* you are doing so that every time the issue hits you can have a detailed list of things that were happening, what you had just done, etc.
It could be that your AV is running an update in the background - it could be that your web browser is going crazy b/c of some sort of attack - it could be that something is hammering your connection from the outside world.
What you have done is the equivalent of telling a mechanic that your automobile arbitrarily stops when driving - the mechanic is going to want to see the car, and if he cannot (as we here cannot physically see your computer) then he is going to ask you a lot of questions, all of which are pertinent to the mechanic b/c it helps eliminate possible causes of the issue but also b/c they may shed new light on the cause. The same applies to computers - we need as much detailed info as we can get b/c the more we know the better we can help you - the better idea all of us will have with regards to what might be occurring.
For example, it could just as easily be a Firefox hangup as it could be a driver issue for your motherboard b/c it is not using the most efficient data transfer method for your HD as it could be a malicious program spiking your computer use as it could be a poorly attached heat sink, which is then overheating your CPU. We cannot know this until we get more details.