It is likely that one of the "hanging" cables is the one to which you connected the WCB3000N and thus why things aren't working. It is not uncommon to NOT connect cables to outlets that aren't being used -- if you connect a cable that runs to an unused outlet, you are sort of creating an antenna thru which signal can leak into your cable plant and cause interference (unless you put a terminator on the connection where it comes up). Depending on where you live and the amount of "noise" in your environment, this may or may not be an issue (I live at the base of a mountain with several radio/tv towers on top and let's just say I can get the local radio station on my toaster at times due to the amount of radio noise).
So, locate which cable it is that runs outside -- if it's near the ONT, open the user side of the ONT and disconnect the coax cable there and attach it along with the cable you located to a splitter and then, using a short length of coax, attach the splitter to the ONT port you just disconnected. Should do the trick.
Optionally, you could insert the splitter where the coax from upstairs runs thru the basement and attach a piece of cable and splitter there to service your basement location. However, this would probably involve cutting and splicing the coax -- which if aren't familiar with doing this properly and have the right tools -- I would not recommend doing.