I don't post a lot of technical support pieces these days, but I tripped over this one and wanted to put it up where I could just send people to it in future. Unless this gets fixed, I suspect the problem will only get worse.
First: the problem. People with Windows 10 are using the default Edge browser. They try to log into a website -- maybe it's an online classroom, PayPal, Ebay -- anything that requires a login. After they enter their credentials, they go right back to the login screen. They go through this loop over and over.
The site is not broken. There's something wrong with your browser.
A browser is the software that runs on your computer that accesses the internet. Windows 10 includes Edge by default, meaning you don't have to choose it, it is just there. If you want to use another browser, you'll need to load one.
If you can't log in, first try clearing your cache in Edge. This appears to be the default fix for most things in Edge. It fixes a lot of problems in all browsers. If you're fighting something weird on the internet -- try this first.
If that doesn't fix it, use the links above and download Firefox or Chrome. Try logging in. Problem solved.
I'm sure Microsoft is working on this issue. Right? I'll leave the conspiracy theories to fiction.