LR3 was not designed to work with El Capitan. But did you clean up after updating OSX. It is usually necessary to trash the prefs. Try this:
Quit Lightroom and launch Finder
On the top menu click go whilst pressing the Opn (Alt) key and then choose:
Delete the file:
Quit Finder and re-launch Lightroom 3. Let us know if that makes a difference.
I had to upgrade to lightroom 6... so let's see.
my lightroom wasn't able to detect the camera device to install the raw files...