The question is in the subject line, but I’ll restate the obvious, as the implication of the ChangeLog was that the “soft reset” button might not work as expected. Reasonable expectations are that a RouterOS box always respond to winbox if directly connected, even though perhaps by mac address only.
Restatement: RB112 was upgraded to 3.0beta7. After upgrade, RB112 can’t be seen by winbox. How does one recover?
Beta7 has not been hanging on any hardware, especially not on a RouterBOARD. I’m sorry, but for now Netinstall is your only option, you will have to find a Windows machine somewhere.
Or use a RouterOS installation CD-ROM (created from the ISO image available). There’s an option to use this as a “live-CD-netinstall-server”, I believe (never done myself, but quite sure there’s an option to do so ).