iPhone 4 won't turn on after screen replacement

Good mornin guys,

I've done many screen replacements on iPhone 4 smartphones (and others!) before, without any issues.

A while back, my phone was dropped, causing the screen to shatter, so I fitted a replacement screen (digitizer) with no issues as usual. Everything has worked fine for months and months.

After upgrading to iOS7, I accidently smashed my phones screen again. It was on and useable, but the screen was shattered.

I decided to replace the screen again (digitizer, as usual), but this time I got the apple logo "screen of death", followed by a 'connect to itunes' message.

I tried restoring the phone via itunes in every mode possible with no joy, but kept getting the "unknown error" message.

After upgrading my iTunes to v11.3, I tried again. After plugging my iPhone into iTunes, it simply said there is a problem with my iphone and I should contact apple.

Now previously, i've had the same issue ONCE before with the first 4S that I did a screen replacement on. After taking it to apple, they looked at it and said the cause was the after-market screen that the phone has detected, and that because not having a genuine apple screen the phone will no longer work and that they will not repair the phone.

Inevitably, I am led to believe they will say the same about this phone.

What options do I have!? I don't understand why it would work absolutely fine untill an after-market screen is fitted, then decide not to start up. I've tried several other screens (smashed but OEM ones too!) but with no joy. I can't believe that a phone can not work because it's detected an after-market screen. I've never had an issue before.

I am very confident with repairing the iPhone 4 smartphones, and would not believe this has been caused by myself during the repair. The only possible thought is that the fall of the iPhone damaged somethign else inside as the rear camera keeps overheating! But this was not the case pre-screen-replatement.

Any suggestions?

Thanks!