my desktop does not read/find my lr3 photos on external drive. the green light is on ,but no folders or collections appear. I do not have this problem on laptop. please help.
In Lightroom, there will be folders shown for a given drive only if the photos on that drive have been Imported into LR. Lightroom will not find these photos by itself.
Have you imported the photos? (And, if it works on your laptop, have you transferred the catalog from the laptop to your desktop, or not?)