Help me! Steam client stuck, steam.exe "Access denied"

[CptWasp]

I'm totally stuck. I was playing CIV6, then exited, then started Rainbow six Siege.
Nothing happened.
I tried rebooting: nothing. Steam doesn't show in the taskbar anymore.
Weird.
I check in the task manager: no steam process is running, apparently, but in details there is a Steam.exe.
I try to terminate it: access denied.
I download the steam client, to reinstall it: it doesn't work! It says another instance is running, but I can't kill the other instance!!!!
What can I do?

[crunchyfrog]

Have you tried rebooting the PC, as that normally kills the hidden process.

[CptWasp]

I disabled Steam from running at startup and rebooted. Now I can launch the installer... but it seems that the installer get stuck near the end!!!
If I uninstall steam I will have to reinstall all the games? I have more than 200 installed games...

[crunchyfrog]

Początkowo opublikowane przez CptWasp:

I disabled Steam from running at startup and rebooted. Now I can launch the installer... but it seems that the installer get stuck near the end!!!
If I uninstall steam I will have to reinstall all the games? I have more than 200 installed games...

No, as long as you don't delete the steamapps folder contents - they're your games. Just reinstalling steam shouldn't touch these.