Here is a general reference that may be relevant to the issue.
http://en.wikipedia.org/wiki/Universal_Serial_Bus 
Hello, it seems that no one has answered your question yet.
Let me give it a try. At first, while reading your post, I thought you were trying to connect your Blackberry to your computer using a Bluetooth connection. But when you mentioned charging it from a USB port, I realized you were talking about something else. Apparently, you wish to connect your Blackberry to your computer with a USB cable. Is that correct?
Based on my own experience, and on the information in the reference given above, there may be some setting you have to change on the device in order for it to communicate with a Windows PC. I have seen this problem on different kinds of mobile devices. What it is called escapes me, but there is some kind of setting that has to be made before the external device in the Windows PC can communicate using the USB port.
The fact that it can get power just proves that the connection is there physically. I have a lot of old dad shuffling around here that will do that, collect physically and get a charge from my PC, but they failed to communicate with a PC and told something strange happens. Either I have to set something inside the device, or have to change the USB cable, or have to try again tomorrow, or have to trick Windows into giving it another try. Hard to explain how that works.
It may be that it's a piece of software you need for your PC, is that for the case I'm sure the manufacturer would have conform to what the proper procedure is for hooking your device to a Windows-based PC. Now if you're using an Apple Mac, the rules are, I think, different. But I'm not sure -- I don't have an Apple here to work on it this time.
Please excuse typos and grammar. I use speech recondition software to post.
