Well I guess I'll try and help, although you are very vague.
First off, I have no clue what you mean by deleting DS Menu, you cannot delete the firmware in the DS, unless you open it up.
Alternatively, you may have just deleted something in your SYSTEM Folder or something is corrupt. Simply go to a site like GBATemp and download the Newest Firmware (unless you have a clone, in that case download an older one or else it will be bricked.)
If the new SYSTEM Folder doesn't fix it, backup all your data like games and stuff on the hard drive and format your card. Format with FAT16 if you have a 1GB or smaller card, but Format with FAT32 if you have a 2GB or larger card.(Just in case you have a lot of files, and it's more efficient with larger cards.)
Now copy over all your games and stuff along with a fresh SYSTEM Folder over.
P.S. Make sure that the SYSTEM folder is labeled EXACTLY that or it will not work and specify no SYSTEM folder found.
If nothing helps here please post back with exactly what you did to your card that you thinked deleted the DS Menu.
