Depends on what you had. You really provided us no information at all. I'm assuming the old SD is completely trashed so you lost whatever was on it/installed.
Grab a new SD, format it to FAT32 for the time being.
If you had an emuNAND the best course of action is to use emuNAND9 (rename it arm9loaderhax.bin) and throw it on the root. Turn the system on and you should be able to get into E9. Then just create a new emuNAND from there. Once done, if you happen to have an emuNAND backup, you can inject it.
Once that's done, you can just copy the CFW files onto the SD and start over. No part of the CFW setup requires your console to actually boot, you can do it on your PC.
If you had sysNAND, just copy your CFW files onto it including the arm9loaderhax.bin and appropriate files.