Compaq Presario 400 Mhz AMD-K6 previously had 128MB & 64MB RAM and very, very sluggish. In hopes of improving performance, installed a 256MB SDRam 133 Mhz in 1st slot w/128MB in 2nd slot and removed the 64MB (3 slots available). After rebooting, only 128MB is detected. What did I do wrong? Help! Thanks.