Setup A Wireless AP To Also Access Shared Drives?

My goal is to be able to login with a few laptops and be able to access internet and our file server's hard drive.

However, I purchased a wireless router and simply plugged this into the main router which allows internet access but does not allow access to other wired computers. If I directly plug the server into this wireless router with this router being wired to the main router, then the wired computers cannot access the server. It's as if it creates its own little network. So, I connected this directly to the main router which gives internet access but nothing else.

(Note: I cannot simply install a new main router.)

I believe I need a wireless access point, but I'm not certain.