Help restoring alt keys to original functions

Hello!

I did something - a long time ago, I don't remember what it was, unfortunately.

I haven't been able to use the alt keys for all that time. They exhibit erratic behavior - I think the left one functions like alt-f4 and the right one... sometimes opens the right-click mouse menu then a sub-menu?

It's hard to pin down, especially when it tends to fool with (or shut down) the file you're in when you're trying to test it.

What I'd really appreciate would be instructions on how to firmly establish what the keys are currently set to and how to compel them to do what they ordinarily do.

My thanks in advance!

Thanks, but - no, that doesn't fix the problem. I tried sharpkeys, too - not sure I used it correctly. These are the inputs I'm trying - just to see whether I can get the alt keys to do SOMETHING identifiable (and non-destructive).

After using Sharpkeys as above, I find that the left alt prints this:

=12:40 AM 3/13/2016'hg\

I think there's more to it than that - moving the cursor up a line?
In windows explorer, it does something I can't identify and whatever's in the address bar.

The right alt? In notepad I wrote

ss
ss
ss

I put the cursor between the two s' in the middle. The first few times I pressed right-alt, nothing. Then, after a few more:

ss
s]s
ss /nb] /nb] /nb] /nb] /nb

...and then just keeps adding "] /nb"

In windows explorer, if I select a file or folder, right-alt just moves me one file/folder down the list.

Update: Replaced the keyboard itself. The alt functions DO work properly - when assigned to another key!
Then I used sharpkeys to eliminate any key changes.
Result (in notepad): the left alt works like alt-F4 (to close a program); the right-alt minimizes the notepad window.
Reassigned left-alt to left alt and right-alt to right-alt, just to be sure - same thing.
Weird.

I'll try keytweak and report!

Update: Replaced the keyboard itself. The alt functions DO work properly - when assigned to another key!
Then I used sharpkeys to eliminate any key changes.
Result (in notepad): the left alt works like alt-F4 (to close a program); the right-alt minimizes the notepad window.
Reassigned left-alt to left alt and right-alt to right-alt, just to be sure - same thing.
Weird.

I'll try keytweak and report!... ok, tried it. Much like Sharpkeys.
Results: I can reassign the left-alt function to the left windows key, which I need less.
I tried reassigning the left windows key function to the right windows key - it won't change.
I can't even turn off the left alt key. When I try, it does: one line up plus "1:27 PM 3/13/2016'hg\"
The set of keystrokes DOES change when I assign different things to it.

I think it's clearly a REGISTRY problem - one that Sharpkeys or Keytweak aren't seeing.

Help?

What might be best is this: can anyone tell me the registry keys that affect the function of the alt keys, and what they should be set to, and possibly how to set them to that?
Although it's odd - the left-alt function works PERFECTLY when reassigned. The more I think about it... it must be physical, yes? But not in the keyboard, which I've changed out for a new one. Bizarre...