I've had this problem on my A4k... The problem I experienced was the SIMMs weren't seating properly because part of the plastic on the SIMM sockets was snapped off. Take all the SIMMs out, check for damage to the socket plastic.
If found, my fix was to apply (using a needle) a TINY amount of superglue on the outside edges to hold the module to the socket.
Oh, and I wouldn't recommend using a 16M SIMM... No combination of SIMMs larger than 4M each worked in my A4k.
