You will need to reformat the SD's card table as MBR, as it might be GTP
*Note, if you select the wrong disk, you are very likely to follow the procedure on that wrong disk, and it will have undesirable effects(destroy all data on that disk)
And I am not held liable if you had bad luck
1) Backup the files you have on the SD card, if you find them necessary
1) Flash GParted in a USB stick, as mentioned in the link
https://gparted.org/livecd.php
2) Put your SD card to your PC
3) Boot your USB drive with GParted
4) Locate your SD card in GParted(probably /dev/sdb or similar)
5) Select "Device"->"Create Partition Table"
6) Select "MBR" in the dialog
7) Apply your changes
Also, a FAT16 partition might be required for DreamShell to work(I am not sure), so create it and put all the files needed(those you had there before)