Only booting up in Darwin

Hello,

My ibook has been booting up only in Darwin(black screen looks like old DOS start up). I have used the start up disk to troubleshoot the software and an error did not surface. I followed the trouble shooting site for apple, but know one could figure out my next step. I did a hardware test ibook version 2.2.1 and the following error message came up: Memory Error detected error code 2MEM/1/4:D1MM1/J7. That was all it found. I took it to the genius bar and the print out they gave me stated "failing AHT RAM test." I dont have the extra cash to get it repaired by Apple. Could anyone help me please. I love this ibook and I want it to last a little longer until I can afford to purchase a new one.

Thank you to anyone who can help.

Samara