DSL can be a little touchy about cable length and quality of cable. It is not the best idea to move it since it is very hard to test and be sure its working.
I would first plug everything back exactly as you had it downstairs except have it upstairs. If it works then you know at least the DSL does not have issue moving.
A couple of things can prevent you from plugging directly into a modem that had a router on it. The most common is that the ISP has placed a restriction on that only your router MAC address will work. You can change your PC to match your router if you work at it. Another is that some DSL connection run PPPoE and you must configure your PC to run this like the router.
You could also just have simple things wrong. Check to see if you are getting a IP address at all... the DNS message will come up with the cable not connected. Also be sure you actually have green lights on your ethernet connection sometime you need different cables.
If you have issues with moving the DSL itself you could leave the modem in the basement and move just the router. You would just need to run a ethernet cable rather than a phone cable upstairs.
Currently my DSL modem (Speedstream 5100) and wireless router (DIR-615) is located in the basement and my desktop is connected to the router via wire. Notebook is wireless and everything works fine. I want to relocate the modem and router to the living room so I can connect the XBox and BluRay player via wires to router. I want to stream from NetFlix through BR player.
I purchased a PCI wireless adapter for the desktop to access network and internet via wireless. I installed a phone jack in the living room to facilitate the connection. My first attempt at this move yielded an incorrect DNS displayed on the notebook when trying to access the internet via wired to the modem directly. I just wanted to make sure that the internet was accessible,. However the notebook has never been connected to the modem via wire previously.
What changes do I have to do and what is necessary for the modem and router to function correctly and network be up and running? This move sounds simple enough but my gut tells me that there's more to it than just unplugging and plugging back in. Can you give me some guidance?