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cant type in dos screen CMD

Here's a good one.

If you cannot type in your DOS CMD screen, first check that the Num Lock, Scroll Lock, Insert or Caps Lock keys on the keyboard are not lit or jammed

If when you type "echo" you see" c:>
then check your "Ctrl" key

I just hit mine hard a couple of times and this cured the problem

If using a wireless keyboard see CHECK BATTERIES