Ok thanks bro, i will try first flashing both main and emmc. If nothing happens, ill try R&D mode. Ill search about R&D more here on TMO.

hi, i flashed both main and emmc by erasing device completely..but still no sign of life.
and when i connected to R&D mode, white led just turned on and stayed but screen was black, so i could not do anything..so i reverted back to production mode.
any idea why?

The "too many reboots" warning points to a software problem, the screen issues point to a hardware problem. Having two simultaneous, unrelated problems is VERY unlikely, but possible...

so it means im done with n9..ok, thanks for your support, ill try some more steps mentioned above again, otherwise ill put it into drawer later. screen replacement is quite expensive for me.

Too many reboots... I remembered while trying unrestricted system ui, i restarted my device at least 15 times everytime after making some changes in ui.. So finally i left my device unused for more than 28 hours , and then i reflashed it, and now its working fine since last 5 hours. No hardware issues. nothing.SO anyone having problem like this, keep calm, watch some movies and give some break to your device.

thanks for the tip dude I had it once but not like your issue so welcome back to your device