biggerjigger,
What gauge wire did you use to connect the power cable to the battery?
Did you check the fuse and fuse holder as well?
Any loose or corroded connection will restrict the available power to the unit.

Since you have a new power cable coming you could go ahead and cut your old one off and connect it directly to the battery just to see if the unit will power up. If it does not than I would get that battery checked (load tested).