A new problem has appeared, in just the last few days:

My Early 2008 MacPro3,1 running El Capitan, will suddenly stop responding to the mouse button and all the keys on the keyboard, despite the mouse still moving the cursor normally. This renders me unable to tell the Mac what to do, so the only solution I have found is to force a shutdown from the power button, since nothing else responds. Generally after restart, everything runs normally for a while, except that after the last restart, the problem recurred almost immediately. Switching mice or USB ports does not help, nor does unplugging the USB for a thirty seconds and then replugging. Resetting the SCM and PRAM does nothing. DiskWarrior can't fix it. Have not tried a different keyboard, so I'll find another to test.

The problem occurs so often at www.HobbyKing.com that that site appears to be either the cause of the problem, or at least a trigger to whatever is. The site is generally slow, and attempting to use its "Search" function results, more often than not, in this freeze occurring upon attempting to scroll down the search results. Could a bad Web page florf a Mac in this manner, or could loading an especially complex page suddenly force access to a bad address in RAM on most attempts? The freeze has also occurred during an online chat with Hobby King, just after loading a link to a particular page sent to me by the chat agent. As I recall, that last was shortly after a search that appeared not to crash. In this moment, I can not confirm whether this has happened at other sites or in other applications besides Opera and Safari, so I'll start paying attention to that.

Is it conceivable that a bad Web site could confuse a Mac with the result that anything key-ish stopped working (mouse button, keyboard keys), while leaving the cursor working normally? Might this be an issue of hardware, rather than software; is the USB on the motherboard, or could it be replaced? Is this a known issue? Here's hoping that this new-to-me problem the Gurus will have seen this before, and know how to fix!

Thank you,