Question Screen-space to world-space in compute shader.

Hi. I'm currently facing issues with the transformation of screen space coordinates to world space coordinates in a compute shader. Briefly said, I'm analyzing the depth texture of an orthographic camera inside a compute shader, finding some special pixels based on calculations, and sending the world space positions of such pixels back to the cpu by an append buffer. I have tried multiplying the screen space coordinates by the projection matrix of the camera ( among other matrixes...) with no luck. All the info I currently have about a pixel is its X,Y coordinate and the distance in world units from the camera. Could you illustrate me the right way to convert these coordinates? Thanks.