Web pages not loading on mid-2009 MacBook

My son uses my old mid-2009 MacBook Pro. Just recently it started doing something odd. It is connected to the wifi network, and network diagnostics says my connection is good. But when I try to connect to anything that uses internet data — any web browser, App Store, games, etc. — nothing works. Web browsers show the most info, so here's what happens… a page will start to load, and then the progress bar stops at maybe 20-25%. Nothing else happens. The weird thing is, if I disconnect wifi, a lot of times the page will load up at that point. Of course, I can't go anywhere after that. I assume the data is being downloaded, but it won't actually load up while the wifi connection is active. But when I turn wifi back on, I still can't get pages to load.

The one wrinkle is that I can use the iMessage application. Including sending files. Does anyone have a clue what is going on? I've tinkered a lot, but I can't figure it out. I thought it might have something to do with the router signal, but the same thing happens when connecting to my iPhone hotspot.