i had 10.5.8, loaded 2gb memory, fired it up and put it thru paces to make sure all worked ok.& it was fine.
loaded 1/3 of 10.6 and stopped w/fail message, I did restart and it began again and further loaded about 2/3rds this time, then fail message again after blackout.. I realized I hadnt turned off screensaver/sleep feature now it wont boot either from old system, old software disk or from the new disk tried holding c key with disc in screen just shows a grey icon that looks like a file folder w/a question mark
returned orig memory-same prob.
Please advise.