OK let's get a couple things straight first.
If you're using Mint:
dpkg is your package manager
apt-get is your automated package tool (enhancement for dpkg)
synaptic is the gui front end for apt-get
With that cleared up,
When you say 'software manager' what do you mean?
I ask because your question isn't clear, at least to me. If apt-get isn't working then neither should any other package install programs.