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Actually, in times past, the installation and/or first run of the Desktop Software did require an internet connection for the PC...but subsequent use of the Desktop Software could be conducted without PC internet access. I do not know if that continues to hold true with the latest version of the Desktop Software (126.96.36.199).
Occam's Razor nearly always applies when troubleshooting technology issues!
If anyone has been helpful to you, please show your appreciation by clicking the button inside of their post. Please click here and read, along with the threads to which it links, for helpful information to guide you as you proceed. I always recommend that you treat your BlackBerry like any other computing device, including using a regular backup schedule...click here for an article with instructions.