I'd guess that you've tried re-seating the RAM, too? Did you put the RAM in the topmost position? Any extra RAM would work its way down. The top 3 support 32 MBs & the bottom one supports up to 16 MBs only.
Does 16 MBs of RAM & higher require that jumpers J1 & J2 be open? The manual isn't clear about this, is it?