Here's a cautionary tale about PC maintenance. It happened to me in April and I thought it was amusing/interesting enough to warrant at least post here.
I noticed my PC developed a new bad habit: when I restarted it (since my reset button doesn't work, I can only power the machine off and then after a bit back on), it started beeping and halting the boot-up process, stating that if I go ahead with booting up the PC, it can lead to harm. In such cases, I had to wait some time (about 15-20 minutes) before attempting turning the PC on again, which I could then always do without any problems whatsoever.
First, I paid no attention to it, thinking it was some overreaction, but when it had happened several times, I thought maybe the CPU is overheating. With that, I started monitoring my CPU's temperature, and it turned out it was rather high to begin with, and you can probably imagine my surprise when, after quitting from some game, I saw the max temperature was 92 C° (197 F°)! You could almost literally boil water with it.
I concluded that either my cooling paste evaporated or, since I hadn't cleaned the machine in more than half a year, the CPU accumulated a bit too much dust. Opening the case revealed it to be the latter case: not only my CPU fan's grating, but just about every piece of grating (and a number of fan blades) in the PC looked like they were coated in sediment.
Dusting the interior of the PC solved my CPU problem, now it operates at a steady 40-45 C° (104-113 F°).
So, people, don't put off cleaning your PC! I was fortunate I decided to give cleaning a chance before my CPU was severely damaged.