Sometimes my right Ctrl-key is locked.
Sometimes also my right Alt-key is locked.

This means, that when I will press only the "Del" key twice
(being unaware of the lock) I will restart Windows unintended.

I found that this lock behavior often occurs after I have
changed the focus to an "MS-DOS" Window (command.com). E.g.,
after having opened such a Window.

I have looked at the settings of my MS-DOS-Window with
regard to special Windows keys, but these settings are all
normal (Windows 98 default settings).

Of course, it is quite annoying that whenever I press my "Del"
key, there is a chance to reboot unintended.

I found that I am able to remove the lock by pressing the
right "Ctrl" and the right "Alt" key once. But this will only
help, after I became aware of the lock.

I have searched the web, but found no report of such a
behavior.

In the last months (for other reasons) I also have bought
several different new keyboards without changing this
behavior, so I know that it can not be a hardware problem of
the keyboard.

I also have temporarily disabled all of the additional
programs usually loaded at startup (such as proxy servers)
without changing this behavior.

It might be some Windows setting or some property of Windows
causing this behavior.

What can I do to find the reason for this behavior?