If you have wired all speakers correctly according to the manual and you still can't get any life out of your subwoofer then it's safe to say subwoofer itself is dead. Also, the 1 year warranty Creative Inspire T6160 has, shows clearly the low build quality of those speakers. Since else-ways, the warranty would be longer,
Just to be sure connect one of the front outputs to the sub input on the speakers. Set the PC to 2.0 so there will be some bass in that output. If you get sound then the problem is in the sub out of the PC. If you don't get sound it's time to contact the seller.