The tips outlined below came from this site.
First, if you can open Photoshop, check to see what hard drive is set up as your Photoshop scratch disk. To do this, go to Photoshop > Preferences > Performance. Then look under Scratch Disks to see which one you are using and how much free space it has. (FYI—I've included these steps for future visitors to this thread.)
Option 1: Delete some files
If your scratch disk is very full (or the free space is low), try deleting some unwanted files from the drive (for me, "Macintosh HD" as seen in the image above) to make room for new ones.
Option 2: Delete temp files
Search your computer for temporary files. These files are typically named ~PST####.tmp on Windows and Temp#### on Macintosh, where #### is a series of numbers. These are safe to delete.
Option 3: Defragment your Hard Disk
I hope one of these methods works for you!
Hello, welcome to the forum!
Since you cannot start Photoshop, you cannot change the scratch disk allocation in its preferences.
Luckily for you, the engineers have devised a shortcut to fix that: Hold down CTRL+ALT(PC) / CMD+OPTION(Mac) as soon as Photoshop starts to get this menu:
Select another disk with more room but do not forget the clean the files clogging up your hard drive, as described in the other messages.
Thank you! This is the first useful answer I've read and I've looked on every other website ever. It's like most people either can't read the problem or refuse to understand.
"I can't start Photoshop because it says my scratch disk is full. I have plenty of space on my drive."
"OK, open up photoshop..."
"First you want to start up photoshop..."
"After photoshop starts..."
"You want to go to the option menu in Photoshop..."
"Defrag your hard drive. I don't know why that would help but I heard about it in the 1990s."
"Have you tried turning it off and on again?"
I am having the same problem.
My "C" hard drive failed and a new one is now in place. I lost all of the installed programs and I am now trying to re-install from disks. I was able to install my Photoshop V.70 from a disk, however when I try to open in I get the above mentioned message "Cannot open, scratch disks are full". I have used the fix of holding down the control & alt keys down while Photoshop opens and it does bring up the Scratch Disk Preferences window. I have three hard drives and all have huge amounts of unused space with the new "C" drive having almost two terabytes of free space. I have tried various configurations of the three drives in the Scratch Disk Preferences window and still Photoshop won't start. It keeps bringing up the message "Cannot open, scratch disks are full".
I should note that I am also having a problem with installing downloaded programs during this rebuild of the new hard disk. My operating system is Windows XP (yes, I know it is no longer supported, however it has done everything I have wanted and so I have kept with it in the new installation). This is just background info if it may help.