I see your new here, so I'd like to welcome you to MacRumors, there are a lot of very knowledgeable people around here that can find a solution to just about any Mac or iOS device problem you can think of.
To help you we're probably going to need a bit more information:
What iPhone do you have?
What iOS version are you running?
What method did you use to jailbreak?
When you plug your phone in does iTunes recognize the device?
Also, you might have a bit more help on this issue if this were posted in the iPhone hacks section.