Yes this tends to be an issue after removing any LCD and reinserting it in small devices such as an iPod or phone. 99/100 times this is fixed by turning the device on and off as the LCD isn't actually damaged it just needs resetting. If this does not work then try it again just to be safe. If you still get nothing then remove the battery and reinsert it. If still nothing then the LCD or the Logic Board has been damaged during the repair, with any luck the LCD is to blame.
Post back with the results and I'll give you another suggestion but chances are the reset will work :)