Very high CPU utilization by all processes

I have a Dell D630 notebook running Windows 7 pro 64 bit. For the past few weeks it will occasionally go into a state where it becomes unusable due to extremely high cpu utilization. In task manager, it is usually msmpeng that is is hogging the cpu when I first look, but if I stop the service and make sure msmpeng is killed, then another process (e.g. Chrome) will take all the cpu. Or if I kill that, then something else. Task manager itself will show as using 50% of the cpu too (its a dual core machine). Seems that whatever process I stop, the next one will immediately consume all the cpu. It is unusable in this state - very, very slow response to keyboard or mouse, and fan is on full blast. If I leave it alone for maybe an hour, sometimes longer, it will return to normal all by itself. If I power it down and do a cold reboot, it makes no difference - within a few minutes it will be back to 100% cpu again. The constant overheating is probably destroying the machine too (once when I tried to re-boot during an episode it immediately shut down due to over temperature). This happens maybe once every two or three days, but seems to be becoming more frequent lately.
Any ideas how to go about troubleshooting this? Could it be bad hardware? Or maybe a system driver? (This thing has a built in NVidia graphics card - could their drivers be the culprit?).

Usually this occurs when MSMPENG is conflicting with another process running on the system... usual culprits are other security software. Since this is the process for Microsoft Security Essentials, make sure no other anti-virus software is present on the system.

After that, I would suggest you uninstall MSE and download the latest version as this mitigates most causes of this issue. If neither of those helps let us know.

Thanks for the feedback, but no luck. As I mentioned, its not just MSPENG that shows 100% cpu, it seems to be any process. I can kill msmpeng, and disable the service, yet it will still show 100% cpu by the next process in the list (e.g. chrome, taskmanager, ...), If I kill one process ,the next one takes its place as the hog. Seems to me it must be some system dll that is in use by all processes (e.g. a video driver) that is stuck in some loop?

And yes, I have all the latest Microsoft anti-virus software and definitions, and there is no other anti-virus software on this machine.

Would it hurt to just try uninstalling MSE (NOT just disable!) and see if the problem persists? Then be sure to reboot. If the problem goes away then try downloading MSE again and reinstall and see if the problem returns.

O.k, trying that. Will let you know if it fixes it. Might take a week to know, since it can sometimes go for that long with having one its seizures!

Have you checked your system to make sure it's free of any bugs that might be lurking in the background. This could be a possible cause.

For the overheating issue, I always use and recommend a chill pad/mat of some sort, just to help. If this is your main PC, then I would suggest that you blow out all ports especially the intake and exhaust ports on a weekly basis.

Sometimes, and I mean "sometimes" a virus, malware or trojan may sneak in there and cause high CPU activity.

Have you tried scanning your system with the free edition of MalwareBytes Anti-Malware?

Its not mspeng - completely uninstalled it, got same symptoms after a couple of days. And yes, I've scanned it with just about everything and don't find much of anything! Starting to suspect it might be hardware related - this Dell D630 has an Nvidia graphics processor that is infamous for overheating and destroying the motherboard. Already been replaced once under extended warranty a year ago. Reason I suspect it is that if I power it down during one of its episodes, the restart it again, it starts acting up within minutes. If I leave it powered down for half an hour or more, then restart it, it's back to normal (until next time). Only thing I can think of is the massive amount of heat is affecting something in the hardware that is causing all processes to peg. Ah well, think its about time to chuck it and get a new notebook (but definitely not Dell).

I was going to mention my opinion of DELL products, but thought better not to do that in the first reply.

I would recommend a Lenovo, Toshiba or Acer notebook as they're ranking among the tops of great quality and builds.