black screen but device works

I replaced 3 months ago the display and touch screen (ifixit kit) and it worked fine.

I have to say ifixit send me twice display because the first time It sent me part with a chip which was weld in different position even if for few millimetres.

Yesterday device has black screen with soft light, It happened during phone call.

Device rings, I can listen to received messages for apps and I can receive phone call but screen is dark.

I tried with soft reset but nothing, If I can try to unplug battery but I have to apply again new gasket for display ! What do you think? It could be problem about new display ?