Hemocytometer grid not visible

​Hi to you all!

I recently bought a microscope Kern OBS 116 for yeast cell counting:

The problem is that hemocytometer grid is visible only on lowest (40x) magnification

After changing objective to 100x magnification, grid can only be be visible as contours

When using 400x magnification there is only white blurred image.

I tried to change condenser and diaphragm adjustment but without success.

Anyone got the idea why it is not working?​