i have a mid-2007 imac running 10.6.8. a few weeks ago i replaced its hard drive. all seemed fine the first week or so but then i started to notice it was taking longer to start up. now, for the last 5 startups in a row i get the grey screen (the apple logo never appears) and nothing else. i've waited upwards of 5 minutes for something to happen but it never does. i wind up doing a hard shut down. then when i restart again, it does so just fine. very strange. so far all i've done is run disk utility but no issues were found. any ideas?