What was the "normal procedure" that you followed?

What do you mean by "deleting the game"?

Normally, you just uninstall it.

There is an option to kind-of "permanently" delete a game from your account -- but that just does a pretty thorough "hide" and you can restore it if you remember that you have it.

What does you mean by "it deleted the files in my collection"? Uninstalling the game is meant to delete the files on your computer -- what else would it be doing?

I uninstall the games with my computer, but the system tells me that the game will delete from my a/c. I need add the game to my account's collection again.
Or I would like to add that the game I uninstalled is a demo. If it is a paid game, will it be uninstalled along with the files in the account after uninstallation?

Originally posted by jy:

I uninstall the games with my computer, but the system tells me that the game will delete from my a/c. I need add the game to my account's collection again.

you uninstall the games thru steam, not thru the computer.

to restore your game to your library, go to
https://help.steampowered.com/en/

enter the name of the game in the search box at the bottom, then select the game, then select "its not in my library"

to uninstall a game, go to your library, right click the games name, mouse over the MANAGE drop down, select UNINSTALL

Originally posted by jy:

I uninstall the games with my computer, but the system tells me that the game will delete from my a/c. I need add the game to my account's collection again.
Or I would like to add that the game I uninstalled is a demo.

Yes, demos will be removed from the library when you uninstall them.