Hello My name is Heather.I'm sorry for what your sister is having trouble with her sub's powering on,but nada is coming from the subwoofer's.well I use to have six ten's in my little Saturn about two years ago and one day pulling out of a store my music just stopped playing out of my speaker's so as me and my best friend was troubleshooting what the !@#$ happend we noticed that all that music my radio couldn't handle and their for my rca's plugs on the radio was blew out the frame..so yes your second guess that you mentioned about it being bad rca jacks on the radio.I would have her go with that being her issue cause it was so mine and I had to replace my very $$costly tv/radio with another and !@#$ it if it did start to play music threw my sub's again.so good luck to her.I know how she is feeling cause I once was there too.