USB and SD card are the common way to input data to the car radio.And people may meet the issues that there's no response when connecting the car stereo through the USB and SD card.So Pumpkin concludes some solutions to these issues.
1.There's no response when insert the SD card.
Solution:
A:There's something wrong with the SD card itself,insert the SD card into the computer to check if it is ok.
B:The format of the SD card is not appropriate.Some guys may have formated the SD card on the Apple computer then the format just can be read by apple computer.All most all of the aftermarket car stereo in the market can only read FAT32.
C:The capacity of the SD card is beyond that the car DVD can bear.Most of the car head unit can support 16GB or 32GB.So maybe you need to change a smaller capacity SD card.
D:There's something wrong with the SD card slot.Well in this case you have to replace it with a new SD card slot.You can ask your seller for a replacement.

2.There's no response when connect with USB cable.
A:Some car radios requires to click the USB icon to enter the USB function,so waht you need to do is to click.
B:Some people connect the car radio with extension cable so it's possible that the extension cable you now use to connect is flawed.So connect it without the extension cable to check if there's anything wrong with the cable,if so change another extension cable.
C: Just like the problems we have met with the SD card,the capacity is beyond the capacty that the unit can stand.So change a smaller one to take it place.
D:The format of the USB flash disk is not FAT32.So please don't format your flash disk or SD card with an Apple computer or the radio is not able to read it.