Bought used & installed BOTH Lcd & digitizer...can't get to power up

Here's the story: Bought Rear Housing and Logic Board on Ebay from a major retailer that sells damaged/returned products/open-box items. Anyway, its 128GB Air A1475 with Wifi & Cellular. I say this because Logic Board is so valuable and do not want to risk any damage. The item is essentially brand new but had extensive damage to digitizer and LCD during shipment when it ORIGINALLY SOLD online to customer.

Which left me buying LCD and Digitizer (with Home Button installed/flex cable). The seller mentioned that a note was made on item that battery may need replacement....apparently someone must have tried to start the product in Itunes. Regardless, I replaced LCD and Digitizer but can't even get this unit to show me a Apple Logo. Frustrating.....

Should I buy a new replacement battery just in case that is part of the problem? I see there may be a backlight fuse that could have been shorted?? Or it that just for the Ipad Mini?? Please advise...Thank you