localhost not working

Question

Hello, I am using VS Code (Cursor) to code a new website I have been working on. It was working fine yesterday, but I shutdown the laptop last night and today it is not working at all. This is the problem:

This page isn’t working

localhost didn’t send any data.

ERR_EMPTY_RESPONSE

I get the same ERR_EMPTY_RESPONSE on every browser I have: Brave, Tor, Edge, Chrome.
I have tried:
clearing browser and dns cache
ipconfig flushdns
a lot of different ipconfig commands, do not remember which ones.
changing the port
used pinging the port (listening)

I can use 127.0.0.1 fine, but localhost is not working properly at all. I have localhost:3001 and still not working (originally :3000) and my backend at port 5000 is also not running.

I'm unsure what the issue is, any help is greatly appreciated!
Thanks!