You hit the Photoshop icon, wait for the splash screen, and then it dies. The error says Could not initialize Photoshop because the scratch disk is full. That usually happens right after you've been editing a massive PSD with dozens of layers, or maybe you had a memory leak and Photoshop crashed hard. You reboot, try again, and the same error. The scratch disk—the space Photoshop uses for temporary files—is completely out of room.
What's actually happening here is that Photoshop uses your hard drive as an overflow for RAM. When you're working on a 2GB file with 50 layers, it doesn't all fit in memory, so it writes chunks to disk. If that disk is nearly full from other junk, Photoshop can't create its temp files and refuses to start. The reason it won't even open is that Photoshop checks scratch disk availability at launch, and if it can't find enough free space, it bails.
The root cause is usually one of three things: your main drive (usually C:) is almost full, the cache folder has grown to gigabytes, or you've got a leftover Photoshop temp file from a crash. The fix is to clear out the junk and then move the scratch disk to a drive with more breathing room. You don't need to reinstall anything, and you don't need third-party cleaner tools.
Fix It: Steps That Actually Work
Step 1: Force-Open Photoshop with a Different Scratch Disk
If Photoshop won't start at all, you need to get past the error first. Hold down Ctrl+Alt (Windows) or Cmd+Option (Mac) immediately after double-clicking the Photoshop icon. Keep holding until you see a dialog that lets you choose scratch disks. You can't change this setting from inside Photoshop if it won't open, so this keyboard shortcut is your only way in.
In that dialog, uncheck your main drive (the one that's full) and pick a different drive with at least 20GB free. If you don't have a second drive, at least select a different partition. Then click OK. Photoshop might start this time. If it still refuses, skip to Step 4 to clear temp files manually.
Step 2: Clear Photoshop's Cache
Once Photoshop opens (even briefly), go to Edit > Preferences > Scratch Disks (Windows) or Photoshop > Preferences > Scratch Disks (Mac). But the cache you want to clear isn't in that panel. You need to delete the cache files that Photoshop stores in your user folder. Close Photoshop first, then navigate to:
Windows: C:\Users\[YourUsername]\AppData\Local\Adobe\Photoshop\[Version]\
Mac: /Users/[YourUsername]/Library/Caches/Adobe/Photoshop/[Version]/Look for folders named Media Cache or files with .tmp extension. Delete everything inside those folders. Don't worry—Photoshop rebuilds them as needed. This alone often frees up several gigabytes if you've been editing video timelines in Photoshop or working with large smart objects.
Step 3: Change the Scratch Disk Location Permanently
Back in Preferences, under Scratch Disks, set your primary scratch disk to a drive that isn't your system drive. The reason step 3 works is that your system drive (C:) is usually the busiest—it's handling the OS, page file, and all your programs. Moving scratch to a separate SSD or even a fast HDD spreads the load and prevents the disk from filling up as quickly.
Select a drive, set it as primary, then restart Photoshop. But here's the catch: if you only have one hard drive, you can't move it. In that case, the real fix is to free up space on that drive. Uninstall old programs, delete large downloads, or move your photo library to an external drive. Photoshop needs around 5-10% of the drive free just to function well, and more is better.
Step 4: Delete Leftover Temp Files from Crashes
If Photoshop crashed hard, it might have left behind temporary files that eat up space. These often have names like Photoshop Temp######## and sit in the same temp folder as your system. Open a file explorer and go to:
Windows: %TEMP%
Mac: /tmp/Search for files containing "Photoshop" or "PS" in the name. Delete anything that's not from an active session. Be careful not to delete files from other programs—just target Photoshop-related ones.
If It Still Fails: Check These
If you've done all this and Photoshop still won't start, you're dealing with something else. First, check if your drive actually has free space. Sometimes Windows reports free space incorrectly due to system restore points or hibernation file. Run cleanmgr to clear system files. Also, check if your scratch disk drive is set to read-only or is an external drive that disconnected—Photoshop won't use removable drives reliably.
Another thing: your user profile might be corrupted. Try creating a new Windows user account and launching Photoshop from there. If it works, your original profile has issues. And if you're on an enterprise machine, group policies might be restricting where Photoshop can write temp files.
One more scenario—you might have a plugin that's forcing a huge scratch allocation on startup. Rename your Plug-ins folder temporarily (to Plug-ins_Disabled) and try launching. If Photoshop opens, you know a plugin is the culprit. Then you can re-enable them one by one.
The truth is, this error is almost always a space problem. Clear the cache, move scratch to a less crowded drive, and you're back in business. But if you're on a single-drive laptop with only 15GB free, no amount of cache clearing will save you—you need to offload stuff. That's not a Photoshop bug; that's physics.