ADE can't find my e-reader

My e-reader worked just fine with ADE 2.0 on my old computer.  It died, and I have a new computer.  Now ADE seems to be unable to find my e-reader.....I can download the books fine, but can't drag them to my reader...I'm running Windows Vista on my PC. My computer guy installed ADE 4.0,, which I uninstalled because I had previous issues trying to run it with Windows Vista.  I'm now running ADE 2.0, which is what I was running before, when everything worked just fine.  Any suggestions?  I'm not a techie person...need some help!  Many thanks....