So, all started when ds1074Z at one day would not boot up and instead starts beeping and flashing all leds. I've tried to reset it by pressing fifth grey button on the left of the screen at the boot time, this helped and i continued to use the scope. This time it did it again, but the scope would not reset. i've tried several time without success. Then i decided to reflash
That means the oscilloscope was unstable/defective before the FW upgrade, then it crashed again during the update, letting it in an unknown state both in hardware and in software.
You should have fixed the hardware first.
Try making a Rigol signed disk like described here (only the last paragraphs at the end, with the instructions written as code, the attached Rigol_sign_disk.zip is right after):
https://www.eevblog.com/forum/testgear/new-rigol-ds1054z-oscilloscope/msg3613778/#msg3613778then try to upload the firmware again. I would try first to re-upload the firmware that worked last time, when it started to became unstable, then if this succeed, fix the hardware defect, then upgrade to the latest FW.
If still under warranty, don't bother trying to fix anything, send it to service and describe what happened.