I have the same problem:
Flashing question mark folder on startup;
No hard drive shown in in disk utility when booted with the OSX installation disk.
Only I've never dropped this computer, but I have moved it around a lot using it as a DVD player.
The computer starts normally if it has been left alone for a half an hour or so, but once you switch it off it's screwed, and you're back to the wait.
The computer gets really hot on top of the screen, but it's some time after the aluminium cools before it will switch on normally- I'm not so sure anymore the two are related.
Anyway, when it does come on it works well to a point, but given any kind of workload (operating a couple of programs at once) it then just loses it, coloured pinwheels and all that crap.
The flashing folder thing started a couple of months ago, but the pinwheels and freezes during operation have started happening only recently, maybe a week or two, and now it's getting BAD!
The kind of bad where you've got about 50gig of personal stuff you actually want to keep, no external drive that works for mac, and the friggin' iMac can't copy stuff onto a big USB card fast enough: It says like, I'm gonna take 35 hours to do this @&@#, man! And then it punks out, cain't deliver the goods, ma neygro, you goe'nhaftacheell the !^$$ out, ya'll..!
This is driving me crazy- What do I do?
During normal ops the disk utility won't finish verifying the drive when it does appear, much less let me press that elusive "repair drive" button.
Anyone! Please Help! If you know anything, say something!