Hey! I attempted to the hardmod as well (on a New 3DS XL), but I'm currently encountering the exact same problem as jad340.
I removed the cables I soldered and doublechecked all ribbon cables multiple times, but don't seem to find anything wrong.
Possibly, I have the same problem with the...
I may try the new ram site, and download more RAM to my Switch. Not sure if ddr3 is the right ram
for it tho. Edit- no it uses floppy Ram, just like @AncientBoi