Camera app has virtual shutter closed after camera replacement?

Check the available memory of the iPod, if you have zero available storage then the camera will not work.

Reset all settings and try again.

the shutter closed is the camera app trying to operate but the logic board is not getting the signal to and from the camera as normal. Once this happens, ie, you removed the camera or the camera was damaged, then the app needs to be reset in order to try again--hence reset all settings. As I recall just a hard reset isn't enough to reset the app.

If this doesn't work, then it is likely that you may have damaged some tiny component that is part of the camera trace on the logicboard....this is very common on the iphone 4 as collateral damage done just by popping off the LCD connector. In this case, check the board carefully especially around the area of the camera connector to see if you can spot a missing capacitor/resistor. Let us know what you find!