HELP! USB issues!!!

A couple of weeks ago my amp went out and through much frustration and irritation, it was replaced. I didn't use the USB port previously b/c my MP3 player is old and wouldn't connect. However after having the amp replaced it dawned on me I could us my phone (motorola cliq) to play music with the USB. It worked for a couple of days and then nothing. The tab on the mode options for the USB would no longer light up. I can still play music from my phones SD card via the aux and via bluetooth, but not the USB. Took the car back in and two days later they are telling me its my phone. Maybe, but considering it worked prior and nothing has changed on my phone I am at a loss.

Today, they called to tell me they were able to hook it up to a ipod and everything worked great! WHY? Mine DID work, so what changed? They suggested I use a stick/thumb drive. Went and bought one, loaded one album onto it and it won't work either. The USB tab won't even light up for me to choose it as an option. I do NOT want to go by a ipod when I have a perfectly great 16 g sd card in my phone that DID work! But I also want to use my touch screen to choose songs and go through my music files without having to use my phone while driving. The USB port is recognizing my phone as it charges it while plugged in. I have tried setting the phone to SD card on, and then off (charge only setting). Nothing causes that USB tab to light up and give me a choice to see whats going on.

HELP. Anyone. I am so irritated. The salesman who I bought the car through did have me try my phone in another pk4 and the other car did the same thing. So at least now I know it isn't my car. However, I also know the USB did work last week!!!!

Anyone? I read the files need to be a certain type, but I am unable to access the type anywhere on my computer that holds the digital music (most all of it is ripped from CDs I own, if that could make any difference in the file formatting?).

TIA!