I don't have much to go on to start giving advice yet. But you may want to check your Norton or Kapersky expiry date as those do shutdown your internet to be on the safe side when they expire. Yes, I've read some unkind words when that happens, and heard too much foul language at the office which they figure that out.
There's also some SIMPLE things that can cause this. Such as the date and time being too far off on your PC.
But again, little detail so I can't offer much. Try the stick on another PC?
I use a Broadband to Go by Virgin Mobil 3G USB Stick for your PC or MAC. I use to get awesome things done on my computer but for the last couple of weeks either with IE or Firefox will work for a few minutes then get a "can not connect to server". I spoke with Virgin Mobil and they said it has to do with my computer. I have done everything I can think of from reading help and support to where don't know where else to go except here because I have always gotten awesome advice that works. Looking forward to some great help gang