Hi, My 17" ALS iMac is not booting (tiger OS). I will preface this by stating the hard drive has been whining and making a lot of noise for the past year or two. Anyway, a few days ago it froze up and I had to pull the power plug. I tried to restart and got a plain gray screen and saw a question mark. Now when I try to retsart I get a plain gray screen with the following message: Invalid memory access at: 0SRRO: (then a long address) WELCOME TO OPEN FIRMWARE To continue booting type "mac-boot" To shut down type "shut down" After I type mac-boot the hard drive (or cd drive?) starts racing quite loudly and then it freezes up and displays a grayish screen with dozens of short, yellowish, horizontal lines and I have to pull the plug again. I have been anticipating a hard driver failure for a while so at first assumed that was the problem, but now I see this memory error and am not so sure. I was planning to purchase a 1 TB drive and maybe upgrade the OS at the same time . Basically I am wondering if I should go ahead and do this or run some additional diagnostics first in case it's something else? Thanks for any input.