Resetting Mikrotik RouterBoard 750GL

I’ve messed up some settings and now trying to reset this router, but the problem is, i can’t. Or at least it seems i can’t.

I’ve tried to use reset button (turning it off, holding reset button, turning it on and release reset button, the moment user led starts blinking, then waiting some time)

I’ve tried to use the jumper (turning it off, short circuiting it with various metal objects and waiting some time, then releasing)
The first thing that struck me, everywhere it says that i should “wait until the configuration is cleared”, but it doesn’t indicate if it’s doing something, instead behaves the same way as if it were simply booting up.

If i knew at least, what to expect, it would be easier, but i’ve done it many times and it still doesn’t do anything.

What’s worse, now it’s dhcp server gives me an ip with subnet mask 255.255.255.255, so i can’t connect to it or do anything.