you all know my previous two questions. Summary that booting Ubuntu is giving black screen and kernel panic in uefi and legacy respectively. So changing boot commandsin grub to acpi=off made it work, but brightness wasn't changing and even wifi was 'disabled by hardware switch' i am remembering a flashback. long ago i updated the bios of this laptop (hp pavilion x360 13 inch i5) but before that i had booted Apricity OS (gnome 3 + arch linux) and it run with no problems. now i just tested it, and bam, same problem as before. balck screen. the bios screwed up something related to acpi. the worst thing is if i try to restore bios nothing happens, because i updated bios long ago, and no where to download old files. help me. where can i download original clean bios files the laptop comes with. :'(
EDIT: right. sorry dude-who-commented. it shows black screen in UEFI (no secureboot) and kernal panic in Legacy. 0x009 somthing. but now i have it sorted. it turns out EVil HP purposely released a bios update which screwed up acpi only for Linux. i downgraded but downloading the old bios and bam! ubuntu works! (typing from Kubuntu 16.04 Plasma 5)
Answer : Went to get drivers for this laptop and clicked windows 8 instead of 10. Found the old driver and installed! Now bam Ubuntu loads! ,Although for future readers, acpi_osi= will also help, but brightness issues! That can be fixed by some programs though.