My linode is offline, I power it on, And then it shuts down immediately.
I followed this guide: https://www.linode.com/docs/products/compute/compute-instances/guides/install-a-custom-distribution/
On how to install a custom OS on linode. I installed Windows. I did everything correctly. Yet, when I power on the linode, it shuts down immediately.
The guide you shared is designed to help with installing custom Linux distributions, so you may want to try again with a guide designed for Windows specifically.
In previous posts on our site, we've shared a specific Guide from GitHub that's extremely detailed and has helped our customers in the past. That guide may have become outdated at this point, so it's possible it won't work, but as of 10 months ago it was still working for Windows 10. Other versions may not work, but this post offers a fix for that.
I'd also recommend searching GitHub, where I found some resources that could help, including an installer with some screenshots to help you follow along:
While we don't support Windows, we do have customers running Windows on our servers, so it should be possible to get this up and running, hopefully with these resources.