I can change nothing

I run 3 different WP sites on one provider. Two of them work fine. The third will not let me do any of the following:

• Install WP version updates
• Install new themes
• Install new plug-ins

In all cases, I get no error message, things just sit there doing nothing.

I somehow think I have some software switch that needs a change, but I really have no idea. I am not a techie — I use my blogs to share info with my students and my family.

I am looking any help I can get.

Many thanks.

Don Simmons