CPU suddenly EXTREMELY sluggish (System Idle Process)

[Technicolor_Bear]

Last January (5 months ago), I purchased a refurbished HP Elitebook 8440p. Here are the specs:

Windows 7 Professional 64 bit
250GB HDD
Intel i5 520M @ 2.40 GHz, dual core APU
4GB RAM

I use it as a gaming computer, and thus far it has worked perfectly fine. Recently, however, the CPU started acting dreadfully sluggish. I was playing TESV: Skyrim at the time, a game which I normally run at about 17-22 FPS (which admittedly isn't that good, but it's the best I can afford on my budget); there was a sudden and horrible lag spike, and I dropped to 4 FPS, but the lag spike never ended. Ever since, my computer has been horrible, and I can't even play anything on it.

I've checked my Task Manager, and I believe the problem is what people often incorrectly attribute to System Idle Process hogging their CPU; please do not lecture me about what System Idle Process is. I know what it is, and I know it isn't hogging the CPU. It's something else I can't see.

I've scanned my computer with Microsoft Security Essentials, Avast!, and Ad-Aware, but none of them found a virus. I have updated my graphics driver. I've tried almost every solution I could find. It isn't Windows Media Player streaming crap either. I've also turned off a bunch of non-Microsoft services. Still nothing.

This is really starting to bug me, and if someone could help, I'd really appreciate it.

UPDATE:
Here's a screenshot of my taskmgr:

 

[OptimusPavlos1]

It being a refurbished pc the worst case scenario is that the cpu is dying. I would suggest using monitoring software to check cpu temps it may be overheating and throttling.

 

[mrmike_49]

4GB of RAM is likely part of problem - 4GB is enough to run Win7 out of the box, but once that clutter starts, 4GB is NOT enough. Check performance in Task Manager, see Memory usage

 

[OptimusPavlos1]

4GB of RAM is likely part of problem - 4GB is enough to run Win7 out of the box, but once that clutter starts, 4GB is NOT enough. Check performance in Task Manager, see Memory usage

You can see at the bottom it says 67% which isn't ideal but shouldn't be causing a slow down.

 

[reedo_43]

Well looking at your pick, firefox is taking 350 megs of ram, steam client is taking a bunch, what ever web companion is is taking a bunch as well. So your 4 gigs is probably being eaten up and it is paging to disk which is very slow causing the lags.You can either end these processes which you are not using to free up memory, or upgrade to 8 gigs. Good luck! Good news is your cpu is not dying!