Xbox boots but does not output audio/video

I was able to fix my issue.

I used windows 10's streaming function to connect to the xbox and reset the video options,

Xbox One has 2 outputs - one HDMI and one Optical Audio (s/pdif). HDMI carries both audio and video. But if you want to send your audio to a receiver that does not have HDMI inputs, then you can use the optical output from Xbox One. PS4 is exactly the
same.

And William is right - if you try converting HDMI to DVI, you will lose the audio on both Xbox and PS4 (unless you are using the separate optical output for audio).

The reason why the regular AV cable is designed to block the HDMI port is that the Xbox 360 cannot output analog video and HDMI at the same time. The differences in between the supported resolutions and the limitations on outputting some video content in
analog HD means they have to shut the analog video output off when HDMI is connected.

There is only one use to having both connected on a traditional Xbox 360, which is using the optical audio output of the old-style AV plug to get 5.1 audio on non-HDMI receivers while sending the picture over HDMI. With the newer Xbox 360 S, this is not necessary
as it already has a dedicated optical audio output on the back. The newer-style AV plugs also lack an optical output from what I know.

If using the regular AV cable this way, there are some problems that can occur. The AV cable identifies itself as such using ID pins in the connector. When the Xbox 360 senses this at the same time as an HDMI connection is active, it gets confused. If the HDMI
connection is dropped - for instance by temporarily switching over to a different input on the TV - the Xbox 360 reboots and starts outputting analog video instead. It may also prevent the Xbox 360 from establishing an HDMI connection when booting up, unless
the TV responds instantly.

There used to be an official audio adapter sold to get optical audio out of traditional Xbox 360s at the same time as HDMI. Those had their ID pins connected to identify themselves specifically as an audio-only dongle. This avoided the Xbox 360 rebooting if
it temporarily lost the HDMI handshake. However, they are no longer made by Microsoft. There are unofficial third party ones, but their ID pins may be wired like the regular AV cable and cause the same booting/rebooting problem.

So if you want to swap between HDMI and regular AV output, the only solution is to plug in only one at a time. If you need separate audio out, try to get hold of an audio dongle that's been proven to work correctly - which may be a bit tricky.

The Nov 27 update seems to have killed digital audio output from my 360.

The boot sound effect when the xbox logo comes up still works in full surround, but all sounds after that no longer work through the fiber optic digital audio output.

From Support:

Basic setup with an audio/video receiver

With an audio/video (A/V) receiver, the best and most direct option is to connect the devices sequentially:

1.Connect your set-top box HDMI output to the Xbox One HDMI input.

2.Connect the Xbox One HDMI output to your A/V HDMI input.

3.Connect your A/V HDMI output to the HDMI input on your television.

Notes

•This option requires that all devices support audio over HDMI.

•Surround sound from your set-top box will not be passed through the Xbox One.

•When you perform this kind of basic setup with an A/V receiver, you’re passing both audio and video through another device. Depending on your equipment, there is a small risk of audio or video lag.