Tom wanted to learn Linux, so he loaded up Linux on his PC. After a month, Windows now wants to install a feature update 1903 and now he's lost a partition. Leo says that Windows is being "bossy," thinking that it's the only OS you should have. So it "clobbers" your boot record and causes a boot-up issue. It's a common, yet complicated issue. You need to have a boot manager to sort it all out. Leo recommends GRUB. It gets loaded first and then asks you which OS you want to use. Most likely, the update redid the master boot record, damaging it. You should be able to bypass the boot manager in the BIOS and go directly to Windows. Once you get Windows booted, then you can start over. Then you can run a boot manager like GAG to fix it.
Leo recommends bypassing dual boot systems and either choosing one or the other or running it virtually.