Gents, here's how I've solved this problem.
Did exactly like khel described in 1st post and ended on blank screen (after "update successful - press any key to reboot") with code 32 on mainboard.
Being anxious and frustrated i've rebooted the PC and got code 00. Here's the fun part: with PC shutoff and USB stick plugged, i've long pressed the "CLR CMOS" button on the back panel and PC powered on by itself, finished the damn BIOS update and all sorted out for me.
Hope this works for you aswell.