Old PC lags on the desktop. (Keyboard and mouse lag)

I have an old AM3+ pc I built a couple years back which was fine until today. I put new RAM in the pc a couple days ago and it worked. Today I put my used WD Black 3.5 in (formatted it); then began to install WoW. the mouse began to lag and my keyboard would spam letters when I would type them. Is it my RAM? I haven't checked to see if the installation of windows needs updating. What drivers would need to be checked for updates for something like this? It's not usable as it is. Any help is appreciated. (Running Windows 10 x64)

Question by Freed88 on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.