Need help after an unnecessary accidental Windows reinstall.

Hello!

The title is convoluted, but it actually makes sense. Picked up a new PC today, and asked the employees of the shop to install my old PC drives in the new machine. In the process, for some reason the PC wouldn't boot up after a restart, so the employee installed a fresh version on a new drive (so that's a total of 4 drives in the machine now), so I thought that was it.

After booting up the machine at home, I discovered that with this fresh install, there is nothing in the apps section, even though my old drives still have everything installed, and I can launch pretty much anything from the respective folders. Annoyed at this development, I decided to see what's what for myself, and tried to boot up the old version of Windows. In the boot menu, I discovered that there were no versions of my old Windows left, nothing to restore or recover. I assume that the employee at the shop probably somehow accidentally nuked my old build, and didn't leave anything behind. To add insult to injury, the installed copy is not even activated.

So now I'm in a situation where I'm considering a full reset of all my drives, and reinstalling everything, as it would just be unnecessary work to try and find everything and reset each individual app. TLDR - is there any way to "discover" the apps I have installed on my old drives?