I continue to get a message saying my scratch disks are full and then Photoshop wont open. Everything ive read about this issue says to open photoshop and go into preferences etc... but if it wont even open up how do i fix the issue?
The scratch disk isn't a Photoshop setting. It's actual physical disk space, and if you don't have any left, Photoshop can't work.
Not only that; when you get that message, disk space is so critically low that you risk the whole machine freezing up completely. You need to take action and free up space immediately.
Photoshop moves large amounts of data around, and there's no such thing as "enough RAM", no matter how much you have installed. So temporary working data are written to disk, and this is the scratch disk.
How much space you need depends on how big your files are, and how many you have open. But realistically, anything below 100 GB is too little and a problem waiting to happen. 500 GB is more comfortable. I'd never go below 500.