I have been having this problem for some time now. Neither my wacom intuos pen nor my lenovo pen that work in Krita anymore. I can draw with my finger, but that's about it. Some brushes still work, but only intermittently... and then the whole program crashes...
The same thing happens with Paint Tool Sai, so I have no idea what's going on.

I SHOULD have all permissions and whatnot. I've tried uninstalling and reinstalling with no success. I've played with the settings and nothing works. The layers aren't locked or anything either.

Can someone help? I really miss being able to draw...

If this is happening in Krita and in Paint Tool Sai with two different styli/styluses then it must be a tablet driver/OS problem. Uninstalling and reinstalling your applications will have no effect.

If you're using Windows 10 then it's probably a recent Windows Update that has affected them. This often happens and there have been recent reports of this happening with Windows 10. You could try uninstalling and reinstalling the tablet drivers (is that what you meant in your post?) or just wait until a corrected Windows Update becomes available and is pushed out to your PC. You could also try asking it to look for an update to make this happen quicker.

Also, see this post: viewtopic.php?f=139&t=155368&hilit=Windows+10