Replaced dvd gears but now the laser and disc spinner are iMactive.

I replaced a friends dvd drive gears (Xbox 360 Elite) fue to broken cog teeth. before thevtrsy was inoperable but the lazer lit up and the dvd drive spun. Now i uave the tray fixed but neither the lazer now disc spinner power on. Is thete a fix? Is there sensor i need to check so the drive realizes iys vlosed? It closes and reopens. Pictures or text to help wpuld be greatly appreciated. thanks