I use winxp for a while on iMac 24" then decided to upgrade to mountain lion so I restarted the iMac by pressing option key. Then flashing folder with question mark appeared. I tried everything option, c, shift, etc. nothings work so I gave up and left it for a night, came back in the morning it loaded up osx fine so I upgrade to mountain lion, fix hd permissions then restart the machine then flashing folder appeared again. I going to take my iMac 24" to the shop to get the hd replace but couldn't help myself thinking, if I didn't decide to upgrade the machine then it still runs fine. Anyone knows what I did wrong?