The function of the 1747-PIC driver in RSLinx depends on the version of operating system you are running, and the version of RSLinx. There was a "hotfix" a few years ago that added 1747-PIC functionality to Windows XP with version 2.42 of RSLinx, but I'll bet that in restoring your computer you don't have exactly the same versions of software as you did last time.
There are numerous threads on this site to read on the topic, as well as multiple A-B Knowledgebase documents.
If you want to pursue a Q and A thread for your particular installation, please begin by describing the operating system, version of RSLinx, type of serial port, and error messages or behavior you are encountering.