@cashaw Sorry for the delay in reply.
Is it possible you never authorized Java to communicate with the Internet? On Windows, the first time you run ImageJ, the Windows firewall will pop up a dialog box confirming that you want to allow Java to communicate on the network. Without allowing this, the ImageJ Updater cannot proceed.
In some cases, I have seen this dialog box appear in the background, so you’ll see it in your task bar, but not popped up over top your ImageJ.