Are you sure that in the Mac to PC conversion of the actual folders, that perhaps some of the names folder didn't change?
Can you compare the exact name of one of these folders on both computers?
What happens if you try to right-click on the problem folders in Lightroom and select Find Missing Folder and then point just that specific folder in Lightroom to the proper folder on your PC?
Yes, the names are the same. Most of the folders relink, but not all. I have tried your suggestion, and it gets stranger. If I just choose just one folder, it links, but all others no longer show in LR, even with the little question marks. The only folder that shows at all is the relinked one. It is really strange behavior.