USB keyboard and sys-usb

My computer does not have a PS2 port. Therefore I have to use a USB keyboard. The Qubes OS setup has not created a “sys-usb” qube by default. Is there a way to use USB devices of any kind, e.g. storage media, on all qubes without “sys-usb”? I have installed “sys-usb” manually according to these instructions:
I then removed “sys-usb” from the autostart.
If I then start “sys-usb” manually, the system freezes and I can only press the reset button. Why does the computer crash when I start “sys-usb”?

EDIT: Warning: you can lock yourself out! Especially if you created sys-usb manually (i.e., not using
“sudo qubesctl state.sls qvm.sys-usb”). Please read carefully the instructions you linked in your post.

Without sys-usb, the USB controller is directly attached to Dom0.
On the other hand, the newly created sys-usb has assigned to it (at least) the USB controller where your keyboard is connected.
When you start the sys-usb qube, while the controller is assigned to Dom0,… BOOM!
Correct way is to enable the autostart of sys-usb and reboot.