Powerbook 15" 1.67 AL. when power pressed to boot, it will go into boot, but then the screen starts flickering from dim to bright a clicking sound is heard, the power cord on the side changes from dark to light amber. the screen then goes to black. some times am able to get to log in then it just goes black. - More information- my harddrive had been making erratic noises for about... 3-4 months. some loud clicking... in thinking that the hd failed i bought a 160gb WD Scoirpio blue IDE drive... These problems still persist. even when i option to start up with my external drive, which i have mirrored my hard drive. it will boot up for the external then this clicking noise as noted above. and then the screen goes black. - thank you very much for any insight.