You may go ahead and merge the catalogs.
Please refer the below links.
Let me know if this helps.
Lets make sure I understand you correctly.
You had a PC with LR. Its catalog was on the internal drive and the images were on an external drive.
You got a new Mac. Installed LR. You started importing images into this new LR catalog.
You now have the PC catalog and the Mac catalog.
You want to merge the two catalogs.
If I am correct, you need to do the following:
Copy the PC catalog to the external drive.
Attach the external drive to the Mac.
Open LR on the mac using your new mac catalog.
Do an "import from catalog", select the PC catalog on the external drive.
Mrinmay Majhi I haven't been ignoring you. I have been trying what Julieanne Kost has been showing in her video blog. So I did what she said but the photos aren't showing up even though I added all the photos. Very confusing.
I don't have photoshop elements. I am now having trouble about my photos showing up in my collections. When I click on the little exclamation mark to direct it to the photo it is referring to it says it is associated with another photo. This is super frustrating.