WHY? Dark blueish black screen. No apple logo. Did hard&factory reset.

Like many I cracked up my screen so I bought a new one. Although my screen was reaallly cracked it still worked and got the job done. I took off my old one and then decided I didn't have the time to do it all then, So I went to put my old one back on for the time being. After I did the screen began to light up in a dark blue but still nearly black color.... There was no apple logo or anything. I still hear the alerts for calls and messages tho, but again, there is no display of anything and the only way I can now turn the phone off is by disconnecting the battery. EVEN now after replacing my old screen with my new iCracked one it is still the same. I've done Hard&factory resets and checked all the connections numerous times. I even disconnected the battery and held the power button down for a little while and let it sit for a few mins, then reconnected and restarted and still nothing.. PLEASE HELP! Thanks..