System Information
Operating system: Win10 64 bits
Graphics card: GeForce GTX 1060 3GB

Blender Version
Broken: blender-2.80.0-git.18e5540a48b6-windows64
(example: 2.79b release)
(example: 2.80, edbf15d3c044, blender2.8, 2018-11-28, as found on the splash screen)
Worked: (optional) 2.79b release

Short description of error
Can't make texture paint to work

Exact steps for others to reproduce the error
I've followed all necessary steps to start painting (as I would on 2.79 and according to this 2.8 tutorial: https://www.youtube.com/watch?v=svzKoq3vew0) on an external image (saved as png) - create a texture on the tools (I tried with single image and material node), save the texture, check the uvs, change to text paint mode (2D and 3D)

I've checked the brush settings, tried to paint in both perspective and image editing views, changed the color, checked modes (texture paint in 3d view and paint mode in image editing view), checked if the texture is connected to the shader in shader view. I can't imagine what else should I check, in 2.79 I would be painting by now.

Is there something else I can do to see if I'm doing something wrong?

Thank you

EDIT: The Draw tool doesn't work when blender is on a non-tablet monitor: I have 2 monitors and a cintiq 13HD, when I dragged blender to the cintiq screen the tool started to work. So to sum up, the exact same setup works in the cintiq, but when I drag the blender window to another monitor it stops working. I tried with mouse and with an Intuos 4.

It even works when trying to paint using the intuos and blender is on the cintiq (although it doesn't work with the mouse, I can't use the mouse to paint in any of the monitors, but the tablets cintiq and intuos work while blender is on the cintiq.)

EDIT 2: It's working now, I don't now what happened, I followed the same steps on a new file and it's working now (after trying for a second time)