I'm not sure if what I'm experiencing is a hardware problem, some sort of virus/malware problem, or even a problem at all.
About a month ago, I noticed that the (processor?) activity indicator (the blue light on the front of my PC) was nearly on all the time, especially when I wasn't at my computer. I initially chalked this up to the knowledge (based on HDD Sentinel warnings) that I had a disk that was likely approaching failure. However, after removing the drive (after it did, in fact, die), it had no effect on the processor activity indicator. The strange thing about this issue is that I've open my Task Manager on numerous occasions while the activity light was constantly on, and there was no abnormal spike in activity with any of the processes listed in the Processes tab. In other words, the System Idle Process was running anywhere from 95-99%, and no other processes were using up any more than a few percentage points of my CPU. Before this issue began, the activity indicator light would only come on when there was some sort of corresponding known activity going on (at least known to me).
What makes things even weirder is that while I'm away from my PC, and the activity light is on nearly all the time, I'll jump on my PC immediately, and while it is sluggish for the first 10-20 seconds, it eventually returns to normal operation, and the activity light ceases from being constantly on (and just blinks in a way that I would consider to be a sign of normal computer activity). I do have a screensaver, but it doesn't kick on until after 45 minutes of inactivity, and the activity light returns to it's constant glow well before the screensaver kicks on. My next instinct leads me to thinking some software title is responsible for this issue, but I haven't changed the installed software on my PC since well before this whole thing started. I feel like the answer for this may be simple and make me feel pretty stupid, but I'm stumped at this point.
I have a custom-built PC running Win7 Ultimate x64. I keep my ESET NOD32 Antivirus 7 up to date, along with any Windows Update patches, and also have Malwarebytes Anti-Malware 1.75 installed with filesystem protection enabled. For a software firewall, I use a program called Windows Firewall Control, which just adds some features on top of Windows' built-in one. I'm behind an ASUS router that is properly (AFAIK) configured. If I need to provide any further info, I would be glad to. Thanks in advance to anyone who is willing to troubleshoot this with me.