i can't install any of my games like shadow of mordor, I've been trying to install this game for over a week and it never finishes loading the installation screen.

Please, does anyone know why this happens?

The game got released on GOG just three days ago...

https://www.gog.com/forum/general/release_middleearth_shadow_of_mordor_game_of_the_year_edition_b5e84/page1

If you're talking about an issue with GOG Galaxy, open a support ticket. I've seen others report that pressing the Install button pops up a window that never finishes loading, but I haven't seen any solutions posted. At least no one wrote back to say if a clean reinstall helped, if I recall correctly.
In the meantime, download the offline installers from your library (or the Extras tab in GOG Galaxy, if that doesn't give you any trouble). Click the game in your library view, then below the blue Download button, click the "Download offline backup..." section to expand it.

If the problem is with the offline installer, then the download was probably incomplete. Try downloading again and double-check that the transfer doesn't get interrupted before it's complete.

Which OS are you using?
How are you installing the games? Through Galaxy or using an offline installer? (Try the latter if the former doesn't work. You can download them on the gog.com website from your account).

Did you check your HD? Maybe it's going bad.

It's probably not the same issues but year ago one of my ram sticks went bad. This caused issues with my games installing. Might want to test the HD and ram.

Let's do a litmus test.
Can you manage to install and run Tyrian 2000?

Issue resolved, I guess.

Turn out he bought new PC. Haha

the c drive needs a lot of space for the offline installers to decompress and then install the game.

Not quite. The TEMP FOLDER needs a lot of space. Having moved temporary files to a ramdrive, i've seen one of the installers where it totally unpacks all the files, then proceeds to copy/decompress/rebuild the files and put them in place. So it might not be the C drive.

I'd almost rather it mount the bin files as a virtual filesystem and then decompress on the fly once, rather than twice. But that's probably too complicated.