I need to deactivate elements 10 on a computer I no longer have.

Elements 10 is 15 years old and way beyond its "replace me" date.

You need a version that's compatible with new equipment.

Photoshop Elements or Premiere Elements (3 year license, no subscription needed).
https://www.adobe.com/products/photoshop-elements.html

you can no longer manage activations using your account.  you must use a computer with an activation (that also meets adobe's security requirements) to deactivate.  if none are available, it's not possible to restore an activation.

Hey there, we have an article on HelpX about how to log into your Adobe account and manage your activations. I hope this can help! https://adobe.ly/3T7ZTDA

I'll copy and paste the steps here, but you can click the link above for more details.

1. Log into your account: https://adobe.ly/3T4uqlG