Win 7 system runs fine and then suddenly slows to a halt

Hello.  I'm having a recurring problem with Win 7 randomly grinding to a halt after running fine for hours at a time.  This is a new problem that has happened 2-3 times a day for the last week or so.  

The system doesn't blue screen, but it runs so slow that it takes several minutes to restart or shutdown.  Any open applications appear to close, but it's running so slow that the icons in the taskbar remain highlighted (as if they are open) for minutes.  It won't actually let me open taskmanager when this happens (it takes a few minutes as it tries and then gives me an error message about permissions and logons).

It happens most frequently when I'm using a web browser.  I mainly use Firefox (v 8.0), but I used Chrome to confirm that it happened outside of Firefox too.  I generally run my browser sandboxed (with Sandboxie), but it's happened without the sandbox running too.

My antivirus scan and malwarebytes scans come up clean. Running the computer's diagnostics, the CPU, memory, and hard drive didn't have problems.

I'm not skilled in computer diagnostics, but it feels like a memory problem to me. I have a meter on the desktop, and when things are slowing the CPU activity stays low (<10%) while the memory meter climbs from ~40% (my normal baseline with no applications running) to about 80%.  I've been so paranoid since this started that I rarely have more than one or two programs running at a time, so I'm not doing anything that should overburden the system.

It's a 1 year laptop with the following specs, so Win 7 shouldn't be killing it:
64 bit Win 7 Pro (Version 6.1)
i5 2.53 GHz CPU
134 GB free of 284 GB

Any help would be greatly appreciated.  I don't know how to find what's killing it since I can't open the task manager when it's slowing down.  Thanks!
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David Johnson, CD, MVPOwnerCommented:
sounds like your cpu is getting overheated and slowing down to reduce heat.  if you don't have any temperature monitoring tools grab speedfan it works, and is very lightweight

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It could also be a hard disk problem. Check event log. May be there are some events with Disk source.

it is better to perform a virus scan in your system with the latest updated antivirus version that should be fine to quarantine any infections if found.

I feel it would be best if you have kaspersky antivirus with latest updates to scan your computer. if you dont have you can own a licensed version it would be cheap

Also clear the temp folder of windows.

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blue1hatAuthor Commented:
Ve3ofa - The heat may be it.  It's a Sony Vaio, and some different Vaio series have had recalls for heat issues.  My fan generally runs pretty hard.  I've installed speedfan and have it set for logging.  50C seems like best case (idle CPU) and much activity pushes it up to 60+.  I will push my computer hard tomorrow to force the slowdown again while watching/logging the temps.  For some reason, running my browser sandboxed always seems to push the computer harder, so maybe I should give that up.

Als315 - I just went through the event viewer and didn't find any hard disk messages.  There were two applications generating a lot of warnings.  I don't use either so I uninstalled those.

Rinil - thanks - I'm coming up clean with any virus scans I throw at it.
open task manager, and select processes tab >view select columns and select the memory related ones
just leave it open when working to see what it shows
speedfan :      
David Johnson, CD, MVPOwnerCommented:
50C seems like best case (idle CPU)   !!!!!!!!!

That is way to hot, is this a laptop?  (noticed that it was) maybe the cpu fan needs a cleaning! make sure all ventilation ports are clear.. I have an i7-2600K and it was running hot because of too much thermal compound between the cpu and the cooler.
blue1hatAuthor Commented:
I will open the laptop up and do some cleaning tomorrow. Just opening several tabs on a browser will push mine up to the low 60s.  Heat management is poor on these - my fan is always loud even in idle (running at 3000-4000 rpm by speedfan).

I reproduced the crash twice today by quickly opening a dozen tabs in Chrome.  CPU spiked high up to about 80%, memory use ran up to 50%, and the CPU and other temps peaked around 62-65C.  I tried this a few more times, though, and couldn't reproduce it.  The computer heated up and the fan took off, but I never lost control and it didn't slow down.

I have one question that's bugging me if this is just a temperature issue.  Once the computer cools down, shouldn't I regain control of it?  During one of the slowdowns, I managed to close the browser and wait for the temp to drop back to about 50C.  I never regained real control.  Everything I did took up to a minute to register with the blue spinning circle just grinding away.    

maybe you have to reboot it to regain control
blue1hatAuthor Commented:
The recommended program was helpful for troubleshooting, and it looks like heat could be the trigger for the described problem
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Windows 7

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