I made a model of my logitech x530 and my monitor, and I can not see them altogether as I was able to 3-4 days ago. I can see them only if I pick them one by one in the link and materials…

Can anyone help me with this ?

Sounds like you may be in Local view instead of Global view. Click the View menu and choose Global. There is also a hot key for this that escapes me at the moment.