So you have a configuration that works one that does not. There is something different between the two configurations that caused the breakage.
The key to troubleshooting is to rule out as many possible causes of that breakage as possible. Once you can determine the cause of the problem you're 90% of the way to fixing it.
You said:
FutureEngineer:
when I integrate the SD memory code, with the keypad and a barcode scanner code, the SD card does not get initialised.
So you made a bunch of changes all at once, thus you don't know which of those changes caused the breakage. This is why it's very important to do incremental development in small steps, testing after each one. It might seem slower at first but in the end it's much faster and less frustrating.