System Very Slow After Upgrade to Windows 10

Hi,

On the night of May 25th my system suddenly shut itself down. I thought it was just installing Windows updates but in the morning I discovered that my system had been updated from Windows 7 to Windows 10, which I had never consented to. A quick Google search showed that Microsoft had changed the upgrade window so that closing the window was now the same as accepting to upgrade.

Ever since the upgrade my system has been sluggish to absurdly slow. I'd say that the "norm" is just sluggish. Windows and apps opening with a noticeable delay. Restarting the computer takes easily 15-20 minutes.

About every 10-15 minutes the system will become absurdly slow for no apparent reason. When I check Task Manager CPU is running at 30-40%, Network 1-2%, Disk anywhere from 5-40%. The only thing that is high is Memory which is 55-65% give or take a few. The biggest memory user seems to be Firefox. Closing Firefox reduces memory usage but only down by 5-10%. The other high memory hog is "System & Compressed Memory" at about 240mb.

About 15-20 minutes after the system has started running in it's absurdly slow state the system seems to revert to it's "norm" state of just sluggishness.

I did a Google search and what I found was to change the paging file size for the C Drive. I changed both the initial and maximum size to the recommended size of 1403mb.  Even after restart (still taking 15-20 minutes) the system is still just as sluggish and still goes through the phase of being absurdly slow every 10-15 minutes.

The biggest problem is trying to watch any HD video. It's very difficult even when the system is just on it's "norm" sluggish speed. When the system goes into snail mode every 10-15 minutes watching any video is impossible. It just freezes and becomes all pixilated.

I'm running a Dell Studio XPS 1640 with Core 2 Duo 64bit processor p8600 @ 2.4ghz and 4.0gb of RAM.

Any suggestions would be greatly appreciated.