i have the same problem, and i fixed it, not all but my infinix is on now,
here what u need to download :
1. [Hovatek] Stock Backup (MTK) for Infinix X551 2GB 16GB
2. flash tool....
after download the ROM
open the flash tool and load the scatter
in flash_tool : remember to unplug the phone first, then click "download" after that plug the phone, and it will running
after its done, unplug the phone and try to press the power button ur phone should start
but!!! u need to go to recovery mode by pressing volume up+power button
and wipe all data, and wipe factory setting, then reboot,
ur device will start
now i have the problem....
1. the baseband version is unknown, already tried to flash over and over but still come with the same problem
2. IMEI is invalid
now im lost