What causes colors to change on 2nd computer?

This is the forum for the mobile app, Adobe color, not Photoshop. However, are you saying the monitor sees the color different? Yes, PC monitors especially change drastically. Most monitors aren't calibrated for color. It will look infinitely different on the screens of your customers as well.

I'll move you to the Photoshop forum.

Dave

Check you color management and color profile settings under the Edit menu and Color Settings. Make sure they are set up the same way.