EP1 won't install

[klaatu]

When I click on "Install" in the dialog box that comes up when I autoplay my (purchased, legal) EP1 DVD, the dialog box disappears and nothing happens. Even with my virus protection turned off. Steam is running and connected. Steam technical support is worthless. Can anyone help?

 

[klaatu]

Just to answer my own post, since it looks like no one else is going to, I tried rebooting in safe mode (with networking, 'cause Steam has to be on) and installing, and that worked.