I accidentally removed power during a firmware upgrade

I accidentally removed power during a firmware upgrade after letting my photon sit for a year in the closet. Now it is flashing yellow which is DFU mode, but neither command line nor the installer seem to recognize that it is connected to USB. Also when I try holding the buttons that are supposed to put it into different modes it only shows magenta very briefly then goes into flashing yellow and doesn’t stop. When you release the mode button when magenta is shown, you get one quick red flash before it goes back to flashing yellow continuously.

Looking for any help in recover this.

What host OS are you using?
What commands have you tried?
When it’s blinking yellow the bootloader seems to be intact so the device should be recognised by the host OS providing you are using a good USB cable on a working USB port.

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I’m with @ScruffR on this one.

I think there are very few people, if any, that have managed to stuff up Photons to the extend I have and running Particle Doctor via CLI almost in all cases (but one where the Photon was physically damaged due to a short) resolved the problem. Providing you can get into DFU mode of course.

If you can enter Safe Mode you can also try Particle Update via CLI, but from what you posted it seems you cannot get into Safe Mode?

Best of luck!!