@ben-erwin wrote:
I would like to rephasize that this isn't function of Photoshop isn't something that should be affected by preferences.
The Preferences file is not just what you see in (Ctrl/Cmd+K) Preferences. The file can become corrupted, especially after a crash or two. Resetting Preferences gives you a clean installation of the application.
You can reset preferences from Preferences > General or by deleting the file or by the keyboard shortcut trick. Photoshop will create a new one when the old one is deleted. The advantage of renaming the file as per Sameer's instructions is that if it doesn't solve your issue, you can restore it. (There is nothing magic about ".old", btw. Just rename it.)
In addition to internal things and the things you see in Preferences, the file also contains actions, swatches, and many other things that you want to make sure you are backup up on a regular basis.
Jane
Thanks for all the suggestions. To be honest, I'm not exactly sure what the fix was in the end, because I did everything! Re-installed PS (for the 4th time), cleared preferences, etc. However, it's source was definitely the installation of the latest version of PS, everything was fine before that and immediately wasn't fine afterwards. It may have had something to do with rasterizing a layer by accident (I didn't need to do, I just accidentally clicked the wrong buttong) and everything went down hilll from there. Many thanks for all the contributions to my original post.