I haven't changed any parts aside from the monitor on this computer in 3 years. And it's really acting up this week. TF2 will corrupt itself on certain servers, Steam is slow and unreliable, firefox is freezing, defragging the computer only made all of the problems worse, and it's had 3 blue screens in 2 days, which is 3 more blue screens than it's had in 3 years. Anti-virus, including malwarebytes doesn't detect anything. I don't know where to start looking for the problem. I don't know why this is in general hardware, but I'm not saying it can't be a hardware problem.