Stuck On Boot After Upgrading (when Root Was Enabled) Mi 2

[miuion22]

Hey, I have just tried to upgrade my mi 2 from "4.12.5 MIUIv5" to the latest miui 6 rom 5.7.9.
It went very well, but when I tried to reboot to system 1 (latest) it became stuck on miui logo.
I found this - http://en.miui.com/thread-130033-1-1.html
I remembered I enable the root permition for a backup app.
How can I fix it now?? The instruction there is for mi4...
Thanks a lot!

EDIT:
Which ROM to use from here:
http://en.miui.com/thread-46133-1-1.html

The warning "These ROMs can only apply to Xiaomi Mi2/2S. MIUI V5 cannot be flashed back to MIUI V4." is very scary

 

[Doc_Samson]

have you tried to enter in recovery and make a new flash from there?

 

[adrenochrome]

beware that after flashing a miui 6 rom, the phone will take very long time for the first boot ("stuck on miui logo" rebuilding dalvik cache), something like five minutes on Mi2S and the progress bar is almost invisible
so be sure you waited at least 10mins before considering reflashing :

when I tried to reboot to system 1 (latest)

seems to indicate that you flashed in recovery mode and that could be your problem : switching between v5 and v6 need to be done in fastboot mode !
boot in fastboot mode (vol down + power) and use miflash to flash a "fastboot" rom from your computer