... and I just entered the triangle-menu of the PS2. Usually the option
"console" (I guess it's "unit" on US-PS2s) says "SCPH-30004"... but
right now it's "unknown".

Strange, strange...
Chris

Was the console ever overheated before?
Was it ever operated in an enclosed space with little ventilation that is
allowed to heat up?

Does the rear exhaust fan work? - Reinhart