Windows won’t boot off internal drives but boots fine off external drives

I am running Windows 10 on a Dell Inspiron laptop.

Today I changed the battery. When I went to boot up afterward, I got a blue screen with error # 0xc000000e . I don’t know whether this was caused by something I inadvertently did while changing the battery or whether this is just a coincidence. (I don’t reboot often, so whatever the problem is might have been there for quite some time and only revealed itself when I went to reboot today.)

Fortunately, I cloned my boot drive (call it drive A) just a few days ago, and (after adjusting the boot sequence in the BIOS) was able to boot just fine off the clone (call it drive B) through a USB port. I then tried the experiment of swapping the drives, so now B is in the computer and A is plugged into the USB port. Result: Now I can boot off A, but I can’t boot off B. In other words, I can boot off either disk but only when they are external. I conclude that the problem is not with anything on the disk. But I nevertheless ran scannow successfully, which (as I expected) made no difference.

What is the best guess for what’s wrong and how to fix it?