iPhone blocked after replacing screen.

For symptoms, see the included image.

My friend asked me to replace his broken iPhone 4 screen.

Here's what I did:

I removed the back cover and the black piece covering the all the connectors. This way I could test if the new screen was working properly, without disassembling the whole phone.

My friends iPhone was password protected, so I tapped the screen until I thought the replacement screen worked fine. I accidentally made the phone lock up, but that was ok, because I was going to disassemble it further. I shut of the phone and removed the battery. Then I went to fixing the phone and after reassembling the phone and turning it on, I noticed the 1 minute wait had changed to a 22 million minute wait. (which is about 42 years, LOL)

Does anybody know how to fix this, without DFU-mode and thus losing all data.

Thanks!