SD Card Reader Not Responding

I'm using the SdFat library to read from an SD card, or at least I'm trying to. I wrote a sketch which I thought would read a line from a text file, then parse it based on a comma delimiter. However, when I ran it, I just got a blank screen.

So I loaded up the 'SdInfo' example from the examples list for SdFat, and put this onto the Arduino Mega, after changing the CS pin to the correct number. When I ran this, it showed the initial prompt on the serial monitor. However, it did not seem to respond when I hit 'enter' or any other character. No error message, no test, nothing at all. I did check the wiring, and it was correct.

There is a bit of other hardware hanging off this Arduino, such as LED display drivers, etc. But during this test, it was only being powered by the USB cable, and the other hardware wasn't referenced in the code, anyway. Could it be that it was just underpowered, or is there something else going on?

how is the reader wired to Mega?

I've figured out what was going on. Turns out it wasn't the input, it was the output. I hadn't set up the LCD screen properly, so it was turning off the backlight. So I couldn't see the output.

This is what I get for trying too much at once. I'll step back and do one thing at a time.