Why do only some DSL ports work for internet in my house?
Have you tested that the problematic jacks are actually wired to your house's phone system? Just take a land phone and plug it in - do you get dial tone?

If you're not getting a dial tone, these jacks are disconnected. Perhaps they were wired to a second line that is no longer active, or simply cut during some other project. To fix that, you'd need to reattach them, tracing the cables and re-connecting them to your main phone service lines.

If the jacks work for phone but not DSL, there may be a DSL filter installed between your main phone line and those jacks. These can be wired inline somewhere, or even built into the phone jacks themselves. Check the jacks first - do they have DSL-related labels? Can you remove the cover and look inside to see if a filter is there? Perhaps they are connected to another jack that has a DSL filter.

If the filter is wired in elsewhere, you would need to trace the wires from jack to your main phone service termination point to confirm.

EDIT: if you don't have active phone service, you probably won't be able to test with the phone/dial tone method. Instead, you can try a tone &amp; probe kit or test voltage on the lines to see if they're connected to your house phone system. Although I'd still try a land-phone test as it's entirely possible you are supplied with a dial tone even if you can't make or receive calls.