White screen after display unit replacement, no apple on screen

Hopefully someone could me out from below situation.

Screen unit is replaced and when turning on only white screen appears. Switches on and off, but only white screen when on. None following:

- Tried to reset by holding power and home buttons long time. Seems to work, but now change on white screen behavior

- Tried to reboot to original setting by holding power and home buttons while connecting to iTunes. Reboot cycle finishes properly, but no change on white screen problem

- Opened again and cleaned connections -> no change

- tried with old cracked display -> no change (even the cracked display worked fine before replaced)

- checked the connections, they seems to be ok

I did not see any damage on volume button flat cables, but they got stress when opened.

What might be the possible cause?

Any help welcome, Thanks in advance, Tinksi