Actually, I plugged AC power after switching jumpers, and run it for 30 secods (that is enough, as far as I know). The same applies to removing CMOS battery. I didn't know, what exactly I had to do to drain all residual power, so I connected AC power, and sometimes even hold power button for an entire process of system's download.
My biggest concern is inability to wake up screen by holding any keys on my keyboard (Ctrl+Esc, F2, F8, F10, Del, doesn't matter), so I can't reach any BIOS settings manually.
Going to try all these steps again today, thank you for your reply!