iPhone 3GS no service/invalid sim help?

[iphoneissues]

Hi everyone,
I just jailbroke my iPhone 3GS about a week and a half ago using absinthe, and have been using a t-mobile sim. It had been working perfectly until today, when suddenly, my iPhone said that I had no service, and when I went to open the sim car slot and stick it back in, a message popped up saying that I have an invalid sim card.

I really need to fix this issue, as I need my phone for work purposes, please help me fix this issue!