Sounds like you either used fonts that weren't NEC compatible, you rushed it and didn't put them on the correct way, or you added more than the board can handle (max 6). There's probably a YouTube vid out there showing it, but simply reading the manual was enough for me.
Here's a link to the
Spark Color 2 page on the NEC website, you can find the Default Files (which should be how SF sent it to you), the Config Editor, and the user manual in PDF. Page 15 of the manual starts how to edit the files.
To simply put it back to default, FORMAT your SD card (which will wipe it clean) to File System: FAT32 and Allocation Unit Size: 16 kilobytes, then drag each folder over from the Default Files individually (so they write in the correct order).