Hi, this seemed like a good site to get help plus it was first result on google. anyways, i've spent around $200 trying to FIX this computer ISSUE i've been having, it's getting ridiculous. Basically my computers been running extremely slow lately. I started noticing hitching in games, it would randomly drop from 85 fps to 40 fps(ut2004, with everthing on lowest settings, a game that i should easily be able to run at highest settings with no frame loss) So i figured it must be a video card problem, so i bought a new video card. nope, still runs the same, $100 wasted, awesome. So after doing some research I thought it might be heating issue, so i check temps in bios and notice cpu running at ABNORMALLY high temps (~75c). So i buy a new heatsync, it significantly brought down temp but I still get hitching in games. ok this is gonna take too long, so ill summon it up. i've narrowed it down. i've either replaced(bought or tried spare) video card, cpu, hard drive, psu, and ram. It's not an overheating issue, not a software issue(formatted several times), so what could it possibly be? Its not just games though, everything runs slow. cpu usage jumps like crazy if i do anything, even dragging window. And when i boot up computer after it's been shutdown for awhile it runs EXTREMELY slow, cpu usage will be 50%+ for no reason, and theres nothing in processes eating resources, so *censored*? makes no sense at all. So I guess i could assume its mobo now, but assuming just hasnt been working out for me. This is extremely frustrating, any help will be appreciated. thanksWhen writing a long post paragraphs can go a long way to readability.

What are your entire specs your computer has now? You can use the following tool to find out in detail, and it might spot some problems:
http://www.majorgeeks.com/download4181.html

Low RAM can cause random suttering, although it shouldn't be this dramatic. You said you replaced your RAM but this does not necessarily you increased its amount.

You SAY the frame-rate drops to 40fps. Are you sure this value is accurate? Games that are on 30fps run smooth.

On the task manager processes, you can sort the list in terms of CPU usage. When you get this spike try to spot which process is USING it.

Make sure your drivers, graphics card and motherboard, are up to date. And that your computer is free of viruses etc.Update: not gonna believe this, but it turned out to be the integrated network card. As soon as i disabled it, cpu usage went from 50% to 0% instantly. so i installed new network card and everythings running fast and smoothGlad you are all fixed up and thanks for posting back.