This is most likely one of two things. The first possibility is that you aren't allowing enough time for the flash to charge. It takes at least 5 seconds for this process to take place but even after 5 seconds you must wait for the red light in the viewfinder to turn off before the flash will work again. The camera won't produce an image if the flash is not completely charged.
If the red light on the viewfinder is off and it is still not producing a flash then it is likely that the battery that is inside the film pack is dead. In this case you will need to replace the film pack.
[[Polaroid Onestep Close Up Troubleshooting]]