If you recently put batteries in it, and you are sure you have it's time is set correctly. Then you may need to press the reset button. Sometimes a Tamagotchi can get a bit glitchy and whacky when batteries have just been changed, or it's just been untabbed. So try giving it a reset.
The other alternative/answer to this - is that it might be dead. Try pressing A and C simultaneously and see if a new egg pops up or not.
With what little info I have to go by, that's the only 2 answers that I can think of.