The XL range has caused confusion before due to the different types that have been sold, you say your device has no SD card and is telling you to insert one, try the following:
Start up Windows Explorer on your computer so that you can see all the different drive letters available on the PC, now connect your XL to the computer without an SD card inserted, you will see a new drive letter appear, right click this and select "Properties" if the computer reports no card inserted then your device has no internal memory, if it does show a pie chart what is the capacity and are there any files/ folders in the drive?
Some XL devices were sold with internal Flash memory and a vacant SD card slot, if yours is one of these it could be just the application files that have become corrupt, or it needs a card and a map purchase - Mike