After a few minutes of running, my computer will slowly start to become laggy?

[Rage Kage]

My computer would have the occasional lag spike every so often, but the other day I turned my computer on from sleep mode, and started to watch a youtube video. All was well until about ten minutes when my video began lagging. I closed the browser and noticed it was not just the video, but the whole computer. As I tried to close some programs to see if that would fix the problem, the lag only became worse to the point where I couldn't do anything. After restarting, it will work okay for maybe ten or twenty minutes before it will begin to lag again to the point where I can't do anything but keep restarting. I've tried running anti-malware, anti-virus, and I updated my video/graphics card drivers. I even have the task manager up when it starts lagging to see if the CPU usage or memory are being used up, but they are not... I'm not sure what else to do.

Running Windows 7 Home Premium
Manufacturer is Dell
Model is XPS 8300
Processor is Intel(R) Core(TM) i5-2320 CPU @ 3.00GHz
Installed Memory (RAM) is 11.0 GB
System type is 64-bit Operating System

 

[xXxPoserxXx]

Have you tried disabling some start-up programs from the task manager's startup tab?

 

[Kisianik]

That is very difficult problem to solve, there is similar to yours in process of deciding http://www.tomshardware.com/answers/id-2758170/physical-memory-increasing-clue-fix.html

So, first question, do you have any antivirus, if yes, run a full scan, next get Malwarebytes free version and run a full scan, let it kill what ever it finds, report.