Windows 7: Shift and Control (not Caps Lock) Key Stuck On - Slow Keyboard Response

I had a problem, in Windows 7, that apparently afflicted Windows XP users as far back as 2005.  For some reason, on a system that did not previously have this problem, I would be typing along and suddenly thE DAMN THING WOuld start and then maybe stop typing in all caps, like that.  A search indicated that a fair number of people were having this problem.

There was the usual assortment of suggested solutions.  One was hardware, notably the keyboard.  I had replaced keyboards and found that didn't solve the problem for me -- not to mention that I was having the same problem, arising at about the same time, on two different computers.  Some observed that rebooting would fix the problem, at least temporarily.  If that was working for me, I would have to emphasize the "temporarily" part.  Some noted that Control Panel > Ease of Access Center > Make the Keyboard Easier to Use might be set to turn on Sticky Keys.

These were not solutions fo rme.  I did a virus scan and found no problem.  It seemed that some rogue program may have screwed things up.  I might eventually figure out which one.  If not, one solution would be to roll back to an earlier System Restore.  But System Restore was not functioning well; I had only a few recent restore points, not predating the problem.  I could do an image restore from some weeks earlier, but I was hoping for something less drastic.

There were some other, funkier suggestions.  One involved a sort of phantom limb theory, like when a person has a bad itch on his/her right arm but cannot scratch it because the arm has been amputated.  The concept here seemed to be that Caps Lock was on when an external or alternate keyboard was removed, so now the computer was still feeling the pain of that setting, and the solution was to plug in that other keyboard and turn off the Caps Lock.  That seemed possible; I had recently plugged in a USB keyboard because my PS/2 keyboard was not responding during a reboot with a certain kind of boot disk.  But trying again with the USB keyboard, with or without the PS/2 keyboard, after reboots, did not seem to fix the problem.

Two other suggestions offered simple solutions.  One suggestion was just to use the other shift key once.  That is, I always used the left-side Shift key, so now I used the right-shift key one time.  The other suggestion was to bring up the On-Screen Keyboard and click once on each of its two Shift keys.  Together, these two suggestions seemed to say that the solution was to use each Shift key on a keyboard, whether physical or onscreen.  (The onscreen keyboard was at Control Panel > Ease of Access Center > Use the Computer without a Mouse or keyboard.)  I found that the physical keyboard solution seemed to work, but only temporarily.

As this problem went on, I learned more about it. It wasn't only the Shift key. It was also the Control key. It seemed to be a problem of slowness. The computer was processing Shift and Control keypresses belatedly. For instance, I would select several files in Windows Explorer, using the Control Key; and then, when I would try to select another one, if I didn't allow time for the system to process the Control keypress, clicking on an additional item would deselect all the others.

A search led to the suggestion that I should see if I had the same problem when using the onscreen keyboard. This seemed impractical, since (as I confirmed in a brief trial) I would not have the same feel through the Onscreen Keyboard (Start > Run > osk.exe). It was also suggested that I see whether the situation persisted in Safe Mode. If there was no problem in Safe Mode, then the prescription would be to perform a clean boot.

It seemed the problem might be due to my KVM (keyboard-video-mouse) switch.  That is, I had one keyboard for two computers.  I switched back and forth by using a hotkey.  It was an IOGear PS/2 KVM.  Right around this time, I did variations on having the KVM connected to only one computer.  My notes are imperfect, but it seemed that this may have made a difference.  I did replace the KVM around that time as well because it was defective, so maybe this stemmed from that.

I also reinstalled Windows 7 around this time.  Maybe that was part of the solution too.  Not sure.