I edited my two models seperately, i wanna make them one.
correct me if im wrong, but you said you cant select your model.
i couldn't make this easier for you.
as you can see on the first image located in the attachment, we have 2 models.
select one of your models right click it and select convert to:
choose editable mesh, as shown in picture 2. (if one of your model is already editable mesh skip this step and move on)
see picture 3 for what you should get in the modify panel.
from here you can modify vertexes polygons and so on.
at picture 4, you can see that i selected the model we converted to editable mesh, go to the modify panel and click attach, when you do that nothing will change, just select the second model and voila, they are both connected.
To confirm that they are both selected, the second model should gain the color of the first model, as you can see now both models are green, and other way is to select any of them and move them, you can see they both move.
and 1 more way to do it is to simply group them together.
Edit: just a quick note, you can convert your model to editable poly as well and it might be better, it only have more functions then editable mesh, but since im used to editable mesh it was easier to explain.