No picture; power LED blinking amber/green...

Subject line says it all. Sometimes when trying to wake up this NEC AccuSync 120 monitor (either by cold-start powering up or just nudging the mouse when in screen-save), I'll get nothing but what looks like a blinking error code from the power LED: 2 green blinks, 2 amber blinks, 2 green, 2 amber, repeating endlessly. If left alone, the monitor will eventually come back on as normal after about 10-15 minutes, and stay normal until its next shutdown (either power-off or screen-saver). Notably, when it does finally wake up, I don't get the usual degaussing pop; it just quietly lights up as if nothing was wrong. Monitor is connected to an HP/Compag Intel P4 with XP Pro SP2; no recent hardware changes or problems of any kind.

This problem has been occurring off-and-on for literally years with this setup. It doesn't happen every time; maybe every few days, though, then weeks with no occurrence. Email to NEC tech support was met with thundering silence, and I don't have a manual for this (an office-issued monitor). I figure that since it's deliberately blinking a 2-2 code at me, I should be able to get that identified; anyone know? TIA...