Hello,
I was upgrading my RB1200 from 5.x to 6.47 via Webfig. After the files uploaded and rebooted the RB1200. Now the RB keep beep every 5-6 seconds and constantly rebooting.
I can't ping, i can't Winbox or WebFig configuration. BTW I don't have console cable with me. Please help how to fix.

Do that netinstall thing

You are brave man ... huge jump ... from 5.x up to 6.47.
Did you upgrade to the latest 5.x version?
Did you read about changes of bridges circa 6.41 version?
Why Webfig? Try Winbox to access your device with MAC.

Once I updated 5.x to 6.x on RB600 and it worked but web interface stayed the same (with old brown-ish webpage) but not functional, webfig would not work, but winbox was fine and worked well. Still ended up netinstalling it just in case...