You want to connect the LINE OUT of your deck to the LINE IN of your PC.
If your mainboard has embedded sound, I'd disable the sound card and try the mainboard LINE IN first because I don't know what that AUX IN is, although it's probably OK.
Speaker out of your cassette deck won't do it.
Then in Nero SoundTrax look for "Insert" - "Import from Audio CD...."
You might have to play with volume sliders....it's been a while since I've
done it.
Did you "CLICK" on the red RECORD button?
Now for some real advice:
I gave up on it as too labor intensive. Not only is it a huge PITA to fool with it as it records, then you have to label, name and tag all the files manually.
So I quit doing that and if I have a cassette for which I want a CD,
I'll just buy the CD.
OTH, I really don't buy
albums, like retail CDs anymore,
I just buy my songs one at a time for 99¢ nowadays.