use ifile on the device or ifunbox from pc or mac to get into device than do this:
Navigate to /private/etc/apt/sources.list.d
Delete the file "cydia.list"
Navigate to /var/lib/apt/lists
Delete all of the files in this folder except the one called "lock"
Navigate to /var/lib/apt/lists/partial
Delete all of the files in this folder
Navigate to /var/lib/cydia
Delete the file "metadata.plist"
Restart Cydia. You should be at the first screen you saw when you first started Cydia: What kind of user are you? Make your selection and Cydia will re-generate the default sources.