Hi Debbie!
If Photoshop was working fine before, then started acting up, there really should be no problem with sufficient memory. Providing you take Dave’s advice about not having a lot of applications open at the same time. To find out how much memory your machine is running, tap the apple symbol at the top left hand corner of your screen, then tap “About This Mac”. It will give you the OS version, processor version, and amount of Memory.
If you already know these steps or tried them, please forgive me, but here is what I was going to suggest to you. If you have some corrupted files on your machine pertaining to Photoshop, they will have to be repaired before it will ever work properly again. Or you may have to do a clean install

of Photoshop, which could be a PITA. Especially if you have actions, etc. that you use. Those would all have to be saved (which they already should be) and reinstalled also. You may also have other issues that you may not yet know about depending what files are corrupted.
So…
First, bring up a Finder window. Go to: Applications> Utilities>Disk Utilities.
When that window is up look in the left hand column. You will see your drives listed. Your HDD, probably your optical drives(DVD/CD) and any other drives you have mounted (external, whatever), or disk images. My internal HDD is labeled by default “Macintosh HD”. The right hand pane will say: “Select a disk, volume, or image”.
Tap (select) the Macintosh HD to highlight it. The RH pane will then come to life. In the four tabs across the top of the center pane (which read: First Aid, Erase, Raid, Restore) make sure the First Aid tab is selected.
Then tap the “Repair Disk Permissions” button. This action may not help the problem, but it doesn’t hurts to do so. Before and after any update, I do this action.
After that runs (and it may take a few minutes depending on the state of your Permissions), tap the “Verify Disk” button and let it do its thing. It should give you a full report on the state of your HDD. It will either say it is okay or its not.
Either way, there are a couple of things you can do from here.
First is start up in “Safe” mode. Rather than me confuse the issue, I’ll give you a link to follow:
http://support.apple.com/kb/HT1564
Another option is use Disk Utility to repair the disk if there is a problem. You cannot repair a drive that you are booted from. So you have to use your original boot disk, the CD’s you originally got with your machine, to boot your machine- Mac OS X Install. I believe it’s the first one (#1). To do this, insert the disk into your optical drive. Restart your computer and immediately press the C key and hold it. The computer will look for a bootable CD or DVD and, if it finds one, will use it as its startup device.
When you have done that and you are booted from the disk, re-open Disk Utility, select your hard drive, and then tap the “Repair Disk” button in the lower right hand corner of the RH pane. If issues are found during the repair, try repairing again. This should solve the issue if Disk Repair shows your disk has a problem. You can then run “Verify Disk” again to confirm.
If it doesn’t here is what I did when I had some issues, Debbie and something I recommend. I am on the road a lot with my Macbook Pro. At home, I keep an updated cloned copy of my HDD on an external drive. Macs support booting from an external HDD so if my internal drive fails, I can still boot and run from the external. Since it is a clone, it is identical to my internal HDD as of last time I updated it, files, OS, and all. Not to sound too "evangelical"

but one of the beauties of Apple machines! So for on the road, I have a 1TB portable external partitioned into two 500 GB partitions. One partition I use to back up photos with, the other I use to keep another clone of my internal HDD so I can have that with me.
I purchased a copy of Disk Warrior (around $100 USD) and installed it on both my internal and the clone copies. This is a wonderful piece of software for Macs and I run it about once a month or so and it keeps things humming. Easy to use and is widely recognized as one of, if not the best, repair programs out there for Macs. Again, you can’t repair the disk you are booted from, so I just boot from the clone copy, run DW to repair the internal HDD, and my problems were solved. Once DW has done its thing and my machine is happy, I update the external HDD clone so I have a happily running updated clone to boot from in case of problems with my internal. This process can save your bacon, believe me, and could help you avoid doing a clean OS install should it come to that. I use a free program called SuperDuper to do the cloning.
DW will not boot a recent Macbook Pro as of now but it should boot your iMac, Debbie, so you use DW (instead of an external HDD or your original boot disk) to boot from while repairing your HDD should you decide to use it. Great program.
http://www.alsoft.com/DiskWarrior/
Now, I’m not saying this will solve your issues but it did mine, and Photoshop is running like it should. And I didn’t have to do a clean install of PS or the OS (thank God!). At the very least you can confirm the condition of your HDD and do it some good.
Good luck Debbie! We’re on your side!
Oh, and by the way? Congratulations to Jan!
