try changing the project sample rate?

I'm a songwriter, been using a Compaq Presario laptop from 1999, no changes to the way I record. I do things the old-fashioned way. Korg X3 left and right audio outputs go into an old open reel recorder as a preamp. That feeds left and right outputs into a stereo cassette deck just for tweaking volume levels. Cassette deck feeds into a switcher that can go into three computers.

I have the switcher set to laptop, as usual. Left and right come out of the switcher and become a single stereo mini into the laptop's input.

I use Audacity. Input is set to stereo. (If I set it to Line in or Aux or mic, I hear the sound (left and right but in mono) but it doesn't record what it's hearing. Just flatline.)

In Audacity preferences, I have it set to "2 track stereo". I have even set it back to mono, closed and reopened Audacity, changed it back to 2 track stereo, closed and reopened the program again.

I am hearing both left and right tracks in my headphones, but in mono.

Last time I recorded a new song, it recorded in stereo as it should've.

This time, it won't. I have tried changing jacks, cords, settings. I've googled, I've done EVERYTHING I can think of. I never changed ANYTHING between the last time I recorded a song and this time.

The stereo feed works from the keyboard to the open reel to the cassette, as two separate tracks. (In this new song, I have two different drumbeats, one in the left, one in the right. This is how I am sure I'm hearing both left and right, but together as mono.)

Can anyone help??? I'm going to have to record just the left side, and then just the right side, and go crazy synching them.