Weird problems

I am running Win 7 Pro 64 bit and it is acting totally weird lately. It freezes every few minutes and even jumps to another page while I'm working. It has done that four times while I was trying to type this far. When it hangs I call Task Manager but don't even have to wait for it to open. I just click cancel and it unhangs. I thought and still think, I must have some kind of extra pernicious malware, but ran four separate malware scanners and none of them found anything. They included Microsoft Malware Removal Tool, Malware Bytes, Trend Micro and Kaspersky. I did full system scans with all of them. I seem to vaguely recall reading that some malware can hide in boot files and not be detected by normal scanners. Is that true and if so, how can I find it and KILL it?

Miles,
Yes I always run a full time security, Kaspersky, which I have used for years with great luck. Last night I booted into Safe Mode with networking and went to Microsoft and got their Malware Removal Tool and did another full scan with it. It still found nothing.
For some unknown reason my computer is doing a lot better today. I'm wondering if it may have schizophrenia or some such thing.

I'd additionally run SUPERAntiSpyware - Downloads
free scanner after declining the trial during install. It roots spyware out of the registry and finds some others will not.

Then check each browsers' Add-On's in its Options to see that only Flash, a Reader helper, and Google search are enabled. A sketchy Search service that's taken over is a big clue.

Next establish a Clean Boot, replace any bloatware AV with recommended free lightweight solution, check System Files, and then start back at the top doing hardware tests to work through all of the Troubleshooting Steps for Windows 7 which will go over your install thoroughly.

Gregrocker,
My computer is functiong well now and I have no idea which of the things I tried fixed it. I suspect that whatever thing, or things, did the job did not take effect until I rebooted and by then I didn't recall what all I had done. The only difference it makes is that it would be nice to know how to fix it if I ever have a similar problem again. I am keeping your reply also in case the problem comes back. Thanks for your effort.