It says my audio drivers are in use with another application. I have no other application s running, and I have disabled Windows' sounds. Neither do I have any speakers or headphones plugged in.
 
My Pro Audio 9 will record, though. So when I shut Pro Audio down, and only Home Studio is running, I still get this error.
when I first opened Home Studio, two days ago, it would record--once.
 
Any ideas what's happening here?

Have you gone to options/audio/advanced, and checked "share drivers with other programs"?
 
What OS are you running?
 
I have Home Studio 2004 running pretty good on two different Windows 10 machines.

Have you gone to options/audio/advanced, and checked "share drivers with other programs"?
 
Yes.
Actually, the error says more:
         "The following driver(s) either do not support the current audio format, or are in use by another application.
         Please choose whether you want to disable them or use them anyway."

What OS are you running?
What soundcard or Audio Interface?
What driver mode? (ASIO, WDM/KS, MME)
What audio settings are you trying to record at?  Higher than 16 bit 44.1 kHz?

OS: Windows 7
Audio Interface: Tascam US 144 MKII

If in options/audio/advanced your driver mode is set to "default", you could try ASIO (probably best), or WDM/KS and see if that makes a difference.
 
I think the "default" setting is always MME drivers, and they usually have limitations of 16 bit 44.1

Well, the audio will arm for recording now. But I didn't do a thing.
 
Sorry for not using proper protocol when posting. I was supposed to have listed my OS, audio interface, and what I had already tried. Sorry for taking up people's time here.
 
Before posting, I had already tried changing the default to WDM/KS. It didn't work. So at your suggestion, I went in to try ASIO. Suddenly, before I even touched anything, the audio track would arm. 
 
Maybe the program is buggy. Maybe it doesn't work well with Windows 7--although I run it as an administrator so that the staff symbols will show.
 
I had this problem years back. I would just close the project down and open another. But I had tried that, and still nothing...till now. I'll keep trying to find the cause and solution to the problem just so I can report back what it was.

Whatever fixed it, I'm glad to see that you've got it working!
 
I've also found that in options/audio/advanced setting the I/O Buffer Size (KB) from the default of 64 up to 256 does a good job of calming down/stabilizing the Disk usage so it's not so jumpy as the track count goes up.

Okay. It's not a bug. The audio would arm because I had
1) changed the driver mode from "default" to "WDM/KS."
2) told the dialog box what to do with the drivers: to "use anyway" rather than "disable." 
 
The audio will not arm if I use the default setting or tell the dialog box to "disable."
 
But then the audio track would not record on the WDM/KS setting. So I switched to ASIO. Now it will both arm and record.
 
But  another problem has arisen: I cannot hear the recorded track on playback. If I save it as an MP3, I can hear the MP3. So the material is in the track, but I cannot hear it on playback.
 
Now I have to figure out why I cannot hear the audio on playback.

Are you monitoring thru the Tascam?
 
It sounds as if you are using the Tascam for audio input but also using the computer's built in soundcard for playback and the built in soundcard does not support the bit depth/sampling rate settings that you're recording at, the MP3 would be 16 bit.