Explanation:
I think that you might have used it a lot or its just a glitch and will come back after some time.
It might be that your screen cracked.
But try re-booting if that does not work, wait and take off the battery.
Right click on the name of the project and press backscape then type hope this helps
Answer:
The relationship between the width and height of a slide
when your threading a bolt no specific kind you should use a die