Windows 7 Home Premium x64 Suddenly Lagging

Good day.

I've been struggling with this problem for a few days and I've searched high and low trying out different methods, but so far no dice.

This problem started last week when I booted up Spider-Man: Web of Shadows. I noticed my FPS dropped massively; I couldn't even turn the camera without huge amounts of lag and subsequent stutter. I rebooted, and then the same thing happened. Then I pulled out my power cord (using a laptop) and removed the battery, and then I let the unit sit for a few minutes. I put everything back and tried it again and viola—it was fixed.

I thought that would be it, but then a day later the same thing happened. This has been happening constantly and the battery-removal method kept fixing it. But now yesterday, it wouldn't fix itself.

Now ALL my games/programs are lagging, despite the fact that they were running swell.

I'm not sure what the problem is, and I've tried several different things:

- Malware cleaners (adwCleaner, Malwarebytes)
- CCleaner
- Windows Disk Check
- Advanced Systemcare 8 optimization (have been using this for quite some time now)
- SFC Scan (said there are corrupt files but couldn't fix them)

The only thing I haven't done is a Defrag, so that's my next move.

UPDATE:

It looks like it has something to do with my AC power supply. I just got a message on the screen after a restart that my adapter is no longer recognized...