I would not be surprised if this was hardware related, like a bad video card, or the memory on the video card going bad, especially if it happens a lot with video. The idea of overheating is also a possibility, or the motherboard backup battery could be going bad and need to be replaced. Other issues could include damage due to static or voltage surges. I had similar symptoms with a desktop after a number of power outages struck in rapid succession.
Have you run CHKDSK with the option to repair? Maybe there are bad sectors in the area where the computer's swap file is stored. This is used for virtual memory, If you have a lot of processes going on that are memory intensive, like video, virtual memory gets more usage.
http://support.microsoft.com/kb/315265
The other possibility is something like a root-kit. I was hit with one of those once, but Malwarebytes took care of it, and since you said you have that, I do not expect that would be the issue.
You may want to check that all of your software is up-to-date.
Try PSI (Personal Security Inspector) from Secunia for making sure that you are at the minimum release for all of your programs for any security issues that could be getting exploited and causing problems.
While things like anti-virus and Malwarebytes will fix problems for things that have been exploited, it is better to close the holes that allow you to be exploited than to keep fixing the problems that crop up due to these holes.
http://secunia.com/vulnerability_scanning/personal/
This will check not only if your Microsoft Windows software is up-to-date, it will check most significant 3rd party software, but you have to tell it to scan all, otherwise it just does the most common programs.
You can also use something like File Hippo to make sure that you are completely up-to-date, even apart from the minimum required for security issues.
http://www.filehippo.com/updatechecker/
An alternative (or complement) to File Hippo is Cleansoft's Update Notifier:
http://cleansofts.org/view/update-notifier.html
I do find that File Hippo gives me less false positives. Cleansoft's product will occasionally recommend that I "upgrade" to a version that is a lower release that what I already have, if they do not update their database quickly enough. As long as you are conscious of this, and know how to check your release level by looking at Properties or Help/About if you have questions, you should be OK.
You may also have things like old copies of Java etc etc that you might want to clean up. If you have Java, you need only the latest release and run-time. These are often left installed when Java upgrades, and they need to be manually removed through Add/Remove programs (and/or via the add-ons function in Firefox or whatever other browser you are using etc).
In any case, at least try PSI and File Hippo. They're easy to use and quite helpful. These are excellent programs even for people who do not have problems, to make sure that you have the latest releases. Some things can be ignored, if you don't use them.
If you are uncertain about the recommendations that these programs make, post what they suggest here, and we can take a look.
BrianIs
AtYou
PS
Microsoft MBSA is also a great thing to run to check for other issues.
http://www.microsoft.com/downloads/deta ... laylang=en
This will tell you about things like missing updates and service packs, which you should already be up to date on if you are running Microsoft update, but MBSA does more. Office product updates. Password vulnerabilities. Policy checks. etc etc be patient. It takes a while to run.