I apologise if this seems too obvious,
Is there an eyepiece in the back of the telescope? Maybe you didnt remember to put one in?
Also, refractors generally need to have the diagonal inserted between the focuser and the eyepiece for the eyepiece to reach focus. If this is not there, you will see a blobby stars but cant get them to focus.
Your description of the front lens group seems normal, perhaps its as simple as the back of the scope not having an eyepiece and/or diagonal in it? It seems that the Tasco 17T may also have an extension tube that may need to be used...found some pics of one
here
Cheers
Chris