Cello — Not working

I brought 2 pin point pens for my final year exam. It worked on my first exam but 2 days later on my 2nd exam it's not working while I have been writing. Then my friend gave her pen which is also a pin point to finish my exam . After 2 days on my 3rd exam again that pen was also not working. But I kept one extra pen that was also a pin point for safety and finished exam with it. But now again this pen is also not working... I don't know what is happening.. it's really terrifying me