Suppose that I have a desktop computer such that everything works except keyboard. Is it possible to install and run Linux to this computer? I guess the answer is no as super user password requires keyboard but I'm not completely sure about this fact. 
Can I do everything on Linux without keyboard?
keyboard;mouse
Actually, you can, as long as the proper tools are installed.A few years ago, I ended up playing quite a bit with a Compaq TC1000 tablet.  It had a detachable keyboard and a stylus.Typing without the keyboard was a bit of a challenge, but I had installed an on-screen keyboard that activated during the display manager login and once my graphical session was established and ready.  This setup used standard Debian packages during the Gnome 2.0 heyday.I typically used it in its undocked mode to either browse the web or to take notes with Xournal.  Xournal's ability to either annotate PDF's or appear just like a legal pad made it very easy to take handwritten notes for later transcription.If standard text was desired, the on-screen keyboard I was using could be trained to recognize your block handwriting, in some ways acting like the Palm Pilot-style Graffiti handwriting recognition, except that you could use your natural handwriting, rather than use a dedicated alphabet.It was functional for a couple of years until the hardware on that tablet became incredibly slow (as software bloated) and then finally died altogether.  I see no reason that a modern touchscreen device couldn't do the same thing.