Problem with gluLookAt

Hello. I have quite strange problem.

while( running )
	{
		
		glfwGetMousePos( &x, &y );
		glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT );
		
		glMatrixMode( GL_PROJECTION );
		glLoadIdentity();
		gluPerspective( 75.0f, (GLfloat)640/(GLfloat)480, 1.0f, 300.0f );

		glMatrixMode( GL_MODELVIEW );
		glLoadIdentity();
		gluLookAt(0,-10,10,0,0,10+vdirection,0,1,0);
		glPushMatrix();

		glPopMatrix();
		glBindTexture(GL_TEXTURE_2D,texture);
		glTranslatef(0,0,5);
		glScalef(5,5,5);
		model2.draw();

		angle+=1;
		if (angle>360) angle-=360;

		glfwSwapBuffers();

		if(glfwGetKey( GLFW_KEY_LEFT )) {
			direction-=1;
		};
		if(glfwGetKey( GLFW_KEY_RIGHT )) {
			direction+=1;
		};
		if(glfwGetKey( GLFW_KEY_UP )) {
			if (vdirection<89) vdirection+=1;
		};
		if(glfwGetKey( GLFW_KEY_DOWN )) {
			if (vdirection>-89) vdirection-=1;
		};

		running = !glfwGetKey( GLFW_KEY_ESC ) &&
			glfwGetWindowParam( GLFW_OPENED );
	}
	glfwTerminate();
	exit( EXIT_SUCCESS );
};

There is a lot of garbage but this is just for experimenting. Now the problem is next:
When xfrom and xto in gluLookAt are equal it doesn’t shows anything at all, only a black screen. If xto is larger than xfrom then it just shows everything upside-down! What is going on?

I think everything is ok - you are underneath something looking up so I would expect it to look upside down. If xFrom == xTo you have no direction to look so I don;t expect anything to work.

So, I need to check if xto is above xfrom and then invert upvector?

The up vector orients you camera around the viewing direction. When look down or up you have to decide what “up” means. Grab a physical camera(or phone) and see what is at the top of the image as you spin the camera.