I bought a PC a few months back and was playing games with it. I noticed every now and then, the keyboard just wouldn't register.
In SC2, I'd press A to attack, and it wouldn't come up till a few seconds later. In Skyrim I'd have trouble walking around. It happens about 5% of the time, so most of the time, I'm able to play fine.
Outside of gaming though, it happens maybe about 2% of the time. For example, I would go to Google , type some stuff, notice nothing was happening, then BAM, 5-10 seconds later, the entire text would start typing. Again, this doesn't happen too often, but enough for it to be annoying.
I changed the keyboard, same problem. I change USB ports, still the same.
I then used my brothers graphic cards (which he reports as having no issues), still the same.
I then update almost everything in my PC. Motherboard, HDD, RAM, and Graphics card.
The only common components are the case and the the CPU.
Yet, even on a completely fresh installation with the HDD free of spyware, viruses etc.
The game STILL occasionally gives me an unresponsive keyboard.
It is so annoying. I use completely legal non pirated versions of the games.