A few days ago I posted about my old PC and there was some interest, here's an update.
tldr: the hdd saved everything! It has windows 3.1 and all the games I remember are still there.
Longer story: I bought a few adapters for PATA/IDE to USB and they didn't work. I had this weird issue where when I plugged the usb into my computer, the drive would power off. You can hear it spinning when it's on, plug in USB, drive powers off. Unplug USB, drive powers back on. So after buying 2 different adapters, I gave up on trying to read it that way.
Then, I got a floppy reader and a bunch of floppy disks. The software testdisk has a DOS version, so I copied that to a floppy and ran it on the computer. While it was analyzing the HDD it told me in an error message that the drive appeared smaller than it actually is, and I should update my bios settings.
After struggling to figure out how to get to bios (ctrl alt s, AFTER BOOTING), I googled my drive model and found the cylinders, heads, sectors information and manually typed that into the BIOS as a "user defined" hard drive, and that was all it needed to be able to read the drive.
After that it booted straight into PC DOS + Windows 3.1 and everything is there. I found recipes, games, and other programs.
I was going to try to send files over serial, but it wasn't working for me (i still haven't tried zmodem yet) but I couldn't even receive an echo to the serial port. So I've been backing things up by copying to floppy disk, then reading the disk on my laptop with a reader.
This sounds like the PSU doesn't have enough watts to go around when you're plugging in a USB device that draws power. You might be able to get USB devices to work if you use a powered USB hub.
No, the reason it doesn't work is that IDE to USB adapters don't support pre-LBA HDDs. These old disks are all CHS-addressed.
I wanted to take images of such disks. I ended up managing to boot an ancient version of Knoppix from a CD (just booting it was a nightmare) and then using dd_rescue to clone it to a file on a CF card connected vi a CF-to-IDE adapter.
Edit: oh, drive powers off when usb is connected? Might be that the adapter doesn't offer enough power, but if you could get around this you would inevitably run into the problem I describe above.