My alt+A become a screenshoot how to fix it?

You really need to learn how to use a computer, at least the words so you can tell people what you have. Any question about your computer has to include what operating system you have and what program you are using. In Windows there is a big icon in the lower left of the screen. It is called "Start". Click that and you get a menu of menus. Click "Control Panel" and you get another menu of menus. You should click on every item in every menu to see what options you have. You don't have to memorize them all, just be aware that they are there. Do the same in every program that you use. Then you can claim to know how to operate your computer at the beginner level.

Ctrl-A selects everything on the screen. Everything turns blue and text turns white. Ctrl-C copies whatever you have selected to the clipboard. Ctrl-V pastes the clipboard into whatever space the cursor is in. Ctrl-X deletes whatever you have selected and also copies it to the clipboard. Ctrl-Z undoes the previous action. Ctrl-Y undoes the Ctrl-X. Other shortcut keys: www.google.com/search?q=windows+keyboard+shortcuts