The missing details mean I'll use what you did reveal.
The fine for hours is a typical sign it's a machine that needs the usual canned air cleaning.
There's also some ISPs that slow down after a few hours of heavy use but only you may know your ISP and if they do that.
This is a problem that has plagued my laptop for some time now, but Im just now able to devote some time to trying to solve it.
Here goes. My computer has developed a problem with severe lag after its been running for a more than a few hours. The thing is, this lag only occurs whole something is being downloaded. The issue becomes worse the longer the computer runs. If I reboot the computer, the problem goes away, but only for a few hours, then the whole process starts again. Here is a video showing what this issue looks like while trying to play a video on youtube:
If I wait around and let the whole video load beforehand, it will play fine, but the video demonstrates what happens when you play the video while it is still loading.
At times, when the issue becomes serious enough, the screen will go black and my display drivers start to malfunction.
Heres what I have tried:
Downloading the latest drivers for my video card
Rolling back the drivers on my video card.
Replacing the memory modules (One of them had stopped working. Adding two new ones did not solve the problem)
As I said, this only happens when downloading, and only after the computer has been running for a few hours. Any ideas as to what could be causing this? Faulty gpu? Failing hard disk?