I had a similar problem last month, I topped up and my cell stopped working, I waited an hour and then decided to take out the Sim card and put it back it in. It worked for a second or two, waited again, Did this a few times over the span of 16 days, it always worked a Sec or Two! Tried to get another sim, thought I did so I waited but it never came in. Finally tried again, and that time I got it. I put the new one in set it up and yes my phone worked! But I am now 16 down from the month I paid for, I have asked on here for compensation but was told to go elsewhere (To another provider) and that it isn't PM's fault the card stopped working (But in fact it is PM's produce that went faulty and without that sim I could not use the phone and what I paid for) I was also told I should have had an extra card ready! I have many friends That have all different Cell phone providers even here with PM and none of them have an extra card! So I guess you can try taking out the card and putting it back in and see if it will work for a few seconds.. If it doesn't then you know it is your card. It doesn't hurt to try seeing that was what happen to me..
