CPU gets flooded, commands go wrong, and/or in wrong order

This usually only happens after a patch, but recently, and across several different games, some horrifically bad; looking at you, Robocraft), my CPU gets jacked-up and inable to process stuff properly. The buffers are filling up fine, but the cores themselves are going all weird. I should point out; I have Intel(R) Core(TM)2 CPU 4300 @ 1.80GHz, 1800 Mhz, 2 Core(s), 2 Logical Processor(s) And normally, on a fine day, running a match of LoL will see a ~92 % (mean) total CPU usage, but recently, it's been on 100% _and beyond._ If something intense happens, like I try to spam all my abilities within 2 seconds, I may, or may not, hear bleep tests having a disco in the Tower, but what definitely happens is: * Trying to move somewhere will always try and position me about 190 degrees down, and that actually includes clicking to places that are off-screen, when my mouse is in the top-right corner or something. * An ability will be shot off in a random direction. * Button presses won't actually do anything, but perhaps instead, (recent example), press Q or E, etc., will actually be translated as a Right-mouse button click. * About 80% of the time, holding Tab to view the score board will keep the board up for a random, extended period, whilst also disabling ANYTHING else from being executed. I literally have to sit and wait 6 seconds or so, after releasing Tab, before I can do something. * A command pressed at the start of a fight will execute some time after the fight's over; Just played Cass, Pressed W and then R, followed by a miasma of E's. Fight lasts 4 seconds itself, 3 seconds later, my ult goes off, but to where my mouse _was_ 2 seconds into the fight. * Sometimes it'll think I still have the right mouse button held down, so will keep trying to do move commands following the cursor. - With other games, say WoW, I'll get brief moments where movement commands stick, like pressing W will keep moving me in a straight line, sometimes off a damn cliff. Holding E for a bit to turn around will see me doing 1000 degree turns, etc. etc. This looks like the two cores are going out of sync with eachother, but an underlying issue seems to be clutter. The problem's been getting progressively worse over the past few months. I'm pretty sure my Motherboard is 10 years old, but unsure; my PC is an assortment of scrap from office computers, and a couple upgrades I've done myself. This could just turn out to be a wear-and-tear issue.
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