cassette tape to cd

Still not too sure about your setup. Is the "line out" of the cassette deck connected to the "line in" of the sound card?

Is it the same make and model of cassette deck you use to play the cassette for listening as you use for recording? (For example, you're using the cassette deck in your car for playback but using a different unit in the home for recording to CD.) You can't expect equal results if you're using different sources for playback.

There is also the chance that your computer soundcard isn't up to snuff. You haven't mentioned make/model for any of the equipment you're using so it is still difficult to spot what may be going on.

Make sure you do not have any "auto level" gain controls turned on during recording. Make sure if the playback cassette deck has a tape bias switch (i.e, regular vs chrome tape) that it is set to the correct position. There may be other hardware switches or software settings that you need to twiddle with.

I use an old Nakamichi 700 MkII into my computer when I need to transfer an old cassette to CD and have no problems with loss of quality

If you get good quality sound when recording LPs to your computer, then the soundcard isn't the problem.

Based on that tidbit of info, it sounds like one of two things. Either your problem is either the cassette deck or it could be that you have the deck's output level mismatched with the line level input of your computer. The software I use for transferring old analog sources is Adobe Audition and it includes an input volume display that lets you know when the input volume is adjusted correctly. Does Nero have a similar feature?

You need to describe your equipment setup and software/settings that you're using for the transfer. That makes a lot of difference in the resulting quality.

It is impossible to offer anything more than the most generic of suggestions without additional info.

You rather blew by some of the questions that have been asked but I'll throw out the following.

The Dell Dimension 1100 is an entry level PC and I believe the soundcard is integrated into the motherboard. The line level analog input of the card could be your limitation. (This assumes that the Onkyo cassette deck is giving good results when you play a cassette back directly through your stereo.)

However, it is still worth checking that you have the correct adapter cable going to the correct input. You should also check your driver and input settings for the soundcard on the PC. I don't use Nero for recording, but double-check your software settings there, too.

Do you have any other analog input sources you can try with the PC (a turntable or tuner, for example)? If you get poor results recording other analog sources to CD then you likely need to look at the computer end of things.

Good luck.

Usually the only ill effect of magnetized heads is a loss of high frequencies, so the tape is a bit dull sounding. However, this would affect playback for both immediate listening as well as for recording.

If you suspect your tape deck, see if you can borrow another deck from a friend. If that works better you know your deck needs to be serviced or replaced.

And, by the way, 12 years isn't very old for a tape deck. My Nakamichi is about 30 years old and plays fine. The only issue you might run into on a 12 year old tape deck (besides keeping the heads and tape path clean) is the heads may be worn if it has been heavily used. Those aren't too big a deal to have replaced, though you'll likely want a service shop to do it so the alignment of the new head is correct.