Krita isn't registering any brushstrokes or eraser marks from tablet and mouse after an hour or so of working fine. Drawing works in SAI. I've tried previously listed fixes which seem to mostly be from several years ago; no accidental selections, tablet driver/computer/Krita are all up to date, OpenGL was off the whole time, and the file is being saved to an external hard drive if that makes any difference. I'm using Win10 on a Dell Inspiron 13-5378. I'd appreciate any help, thank you!

I think the first step should be to restart krita and create a New File, to avoid any complications with accidental selections, layer blending modes or layer opacities.
Then make sure that the transparent paint layer is the selected layer in the Layers docker.
Then select the b) Basic-2 Opacity brush preset from the Brush presets docker and make sure that the selected foreground colour is not white, choose a saturated dark colour.
Then try drawing with your mouse or stylus and see what happens

That seems to have worked, doing that and returning to the original file somehow fixed everything. Thank you!