Contour box keeps rebooting.

moved my box to other side of room.  The cable was not long enough to reach so I bought a longer one to connect to the wall outlet.  Box kept rebooting because of no signal detected.  So I reattached the shorter one diagonal across the room (trip hazard ) and the box booted fine.  The short cable that works is about 15’ the long the one that doesn’t is 20’ long.  I used both cables on the internet router with no issue, however only the shorter one works with the Contour box.  Do I need to have Cox install a new run and outlet?  If so what does that cost on average?  Other info is that my internet line is dedicated from the outside box while the tv is on a 3way splitter at the outside box.  Much tanks to those who reply!