Get your way to the file and directory structure of your iPhone (through SSH or iFile or Mobile ..)
Look for the /var/lib/dpkg/ directory
You should be able to find the following files: available, availble-old, status, status-old
Rename "available" to "available-bak"
Rename "status" to "status-bak"
Rename "available-old" to "available"
Rename "status-old" to "status"
Start Cydia , make sure that you allow Cydia to load completely first (just to be on the safe side ), try to install some apps