Load two or more volumes butonly one visible at a time

Using Fedora linux -
Had to install Slicer on new computer from scratch (4.8) , other later versions have problems to run .
things look fine .
However if i load two or more volumes , only one show at a time even if both “eyes” are open
is it a hardware problem , or am i missing something . - how can i fix it
it mean i cannot superimpose one volume on another .
please give advice

First you are using a version that is not supported anymore. So, you may want to spend sometime on how to get the newer versions working your computer.

Are these two volumes acquired at the same exam (e.g., T1 & T2 images) or are they co-registered already.

If so, you can set one as the foreground volume and the other as the background volume and visualize them together, by changing the opacity (alpha) channel.
See this for more detail: