I had this - my 2599LMT-D has gotten "soft" (I hope) bricked. By doing as you said I finally got the connection "noise" and at the same time the word "SYSTEM" appeared above the Garmin logo and scrolled down for a short time (the first time, it then changed after a few seconds to "LOADING") - and I managed to get a reasonable message (Unit ID redacted) of:
Code:
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