I just responded to your latest email, but I will post it here as well:
Couple thoughts: What power supply are you using with your Neo Geo? Is it an original SNK power supply, or a 3rd party one? Can you post a picture of the power supply you use with it?
The NeoSD and NeoSD Pro are designed to work with original SNK power supplies and if you are using 3rd party ones sometimes they don't have enough power for it. Even if an original cart works fine, the PSU still might not have enough juice for the NeoSD.