high Sierra will not come up on the App Store. What do I do?

Okay, so I've been working on my school's computers. They're old, like 2010. Last week I was able to fix 3 of them, wipe them out and upgraded them to macOS High Sierra, because they're compatible with the Adobe CC 2018. I've tried to connect with the link that takes you to download High Sierra on the App Store, but for some weird reason, it won't take me there. It worked last week, and now it's not taking me there- It just leads me to the home page. Any suggestions on what I can do?