Never seen an A1200 doing this before!

[Karlos]

Sounds like whatever makes the power LED light up in dim mode is malfunctioning (power LED is generally supposed to be dim for a second or two on powerup before going bright on a 1200, correct?)

Isn't the power LED brightness level supposed to indicate the status of the low pass audio filter?

[Karlos]

Weird. My hard disk light doesn't work at all.

Assuming you have a working hard drive installed, have you checked the little circuit board that the LED's are on? I've had one or two of these "fail" over the years where a solder connection cracked.