I have an iMac that I've used PE 11 successfully for a couple years. Suddenly it's come to a grinding halt. When I try to edit anything it slows to a crawl, then just stops working all together.
Here's what I've done so far:
Updated my Mac to OS X 10.10.2
Cleared cached files
Made space on my hard drive
Uninstalled, and reinstalled PE 11
An interesting symptom I've noted as it goes down the tubes:
The windows such as Project Assets stay in the foreground if I use another program while waiting for it to think about doing what I asked it to, for example; play the clip that I'm trying to edit. So as I'm looking at my mail, the PE dialog boxes will be in my way.
Yosemite sometimes has problems, often related to "default" permissions needing to be changed
-one person's solution https://forums.adobe.com/thread/1689788
Did you specifically delete the Adobe Premiere Elements Prefs file in your Premiere Elements 11 Mac?
I believe the path to that file should be
Libraries\Users|Owner\Application Support\Adobe\Premiere Elements\11.0