Question Mark in Flashing Folder at start up problem.
After trying to fix the flashing question mark folder problem, I took my iMac to the Apple store and, naturally and a little embarrassingly, the iMac booted up just fine and everything seem to be intact.However, when I brought it home it reverted but to same problem i.e. question mark in flashing folder. I read and tried most suggestions I could find but still cannot get the iMac to startup. I tried holding down the "C" key, then the Option key, then PRAMed it and even attached the separate back up disk I use as a Time Machine for my new iMac. IThe problem Mac is a 2008 iMac though I don't exactly know which OS came with it, in any case, I cannot find the original disk. The iMac is networked with my latest iMac. Can anyone help? Thank you.
iMac, Mac OS X (10.7)