led turns red when I plug in the av or hdmi cable

Hey there, generally red lights around the power button means the console has failed and will need a repair.

You can try the wizard at this link to diagnose yourself:
support.xbox.com/.../flashing-lights-solution

If you have no luck there though, you can do the repair through here:
myservice.xbox.com/.../Welcome.aspx

I had a similar issue with this on my older Xbox 360. I had to use the HDMI for the TV/Monitor and the AV Cable to plug in my headsets through the Digital Optical on the AV Cable. I had to use the HDMI first, and go into the system system settings and
change the display properties from 1080p to 1080i or even down to 720. Then turn off the console, hook the AV cable into it and boot it back up. Hope this helps!

If not are you using the standard AV Red/White or Optical cable? and which Xbox 360 are you using?

So just to summarize, the HDMI cable works when the AV cable is not plugged in, but when it is I get no signal.

The one designed to sit alongside the HDMI cable?



Plugging in a regular AV cable, like the Composite or Component AV cable, disables HDCP over HDMI. The thin AV audio dongle does not...

This hurts to read...



First, some history: from Launch until September, 2009, all HDD-equipped consoles came with a Component AV port cable. Component cables have two cable clusters. The first cluster has three RCA plugs colored red, green, and blue. The second cluster has three
RCA plugs, colored yellow, red, and white. On more than one occasion, I've inadvertently swapped the green and blue Component AV port cable RCA plugs when connecting to a display device. It's why I use a flashlight now when wiring up Component video. In the
dark behind a TV, it's easy to get blue and green Component jacks mixed up.



From Launch until September, 2009, the low-end consoles (Core, Arcade) came with a Composite cable that fits in the AV port. It only has three RCA plugs at the other end - yellow for Composite video and red/white for audio.



From September, 2009, onward, the only video cable included with 360 console kits is the Composite cable.



HDMI's a completely different cable that goes into the HDMI port, below the AV port. HDMI cables were included with Elite console bundles and most Special/Limited edition consoles prior to September, 2009 (with the notable exception of the Halo 3 console). Consoles
that came with an HDMI cable also included a thin AV port dongle to provide left/right and optical audio out.



Anywho, to sort this out we need to know exactly which cable is being used with the console - Composite, Component, or HDMI? From what is being described, it seems a Component cable with swapped green/blue plugs, but it would be nice to know for sure.