Here is how i solved problem when PC game or other process frozen the way that it prevented any other process (even task manager) to be visible (frozen game window was sticky on the foreground).

TestDriveUnlimited PC game happens to froze sometimes the way that after doing command Ctrl + Alt + Del, it shows the game window and start menu, but it do not show Task manager or any other process after doing Alt + Tab. Frozen process was the only thing visible.

Ctrl + Enter
Alt + F4
Alt + Esc

it do not close the game.

There is possibility to use command Win + R to run command prompt. And enter command:

taskkil /F processname

I had to do it blindly as game was always on the foreground. But in my case it did not worked to kill process. Using Alt + Tab i was able to see other programs screen thumbnails.

What helped was to install program SystemExplorer (before frozing happen) and then when game is frozen, i do Windows key.
Then i start typing into the search field: Syst. and it shown SystemExplorer so i hit enter to run it (if search field in the start menu is not available for you, try to use arrow keys and enter key to navigate thru the start menu to run SystemExplorer from there)

Once i run SystemExplorer, it started on the background behind frozen game window. But using Alt + Tab i was able to activate that window even it was invisible behind frozen game and i did not seen it even it was active (i seen program was launched in thumbnails when doing Alt+Tab). And i started typing frozen game name while SystemExplorer window was active (was invisible) and hit enter key, then by Alt+Tab i verify it found/filtered only one process (hanged one). Make sure you activate SystemExplorer windows using ALt+Tab. Then i do Tab key to highlight process and then do Shift + Del to forcefully kill the highlighted process.

That was really blind game, but i was not prepared to loose changes made in the opened programs by resetting computer.