So you're probably wondering what I mean by this. What I mean by this is I am unable to get through Scratch Disk Preferences to get to photoshop proper. Whenever I open up Adobe Photoshop I get a window (the aforementioned preferences) showing my scratch disk location and that it's full. Whenever I press OK it closes Adobe. When I hold Ctrl+Alt it just shows my single Scratch Disk, with no way to change it, and when I press OK it just goes back to the scratch disk preferences window.
I'm basically stuck in a loop where I can either not hold Ctrl+Alt and be forced to uselessly press OK to close the Scratch Disk Preferences window and Adobe entirely. Or hold Ctrl+Alt to get sent to another window, that shows no way to get to Photoshop proper to change my scratch disk, where I can only press OK to go back to Scratch Disk Preferences so that I can press OK to close Adobe and the Preferences.
I also just started using Adobe Photoshop. I got the Free Trial hours ago.
Photoshop will use approx 5GB on opening so you need at least that space on your chosen scratch disk. If you haven't got that space and it is your OS disk then you really are in trouble and will soon experience much bigger problems than Photoshop's message. You urgently need to clear space.
As far as Ctrl+Alt on start up - that will show you all disks available to use as scratch and provided there is more than one, you can choose the scratch disk there just as you could in Photoshop preferences. It will not usually show you removable drives, such as SD or CF cards, as Photoshop would crash if they were removed with Photoshop open. It will also not show unformatted drives.