I have done FORMAT + DOWNLOAD A850 ROW rom to my Lenovo A850. But sadly, it is the wrong firmware. Supposed I need to select CN rom to my phone. After flashed ROW rom, the phone is dead = not detected by PC when connected with USB cable, no boot up.
So, I googled for solution, and found out with this link.
1)
http://forum.gsmhosting.com/vbb/f672/lenovo-a850-dead-boot-how-easy-jtag-1868940/index2.html
2)
http://forum.gsmhosting.com/vbb/f672/lenovo-a850-dead-boot-how-easy-jtag-1868940/index2.html#post11469369
So, my solution based on those links is:-
1) Power off phone.
2) Press VOLUME UP + VOLUME DOWN while connecting USB cable to PC and phone.
Now the phone is detected by PC and I can flash another rom then.