Flashing Folder Icon on boot

FYI, I had the same issue (Couldn't find the HD with Disk Utility, or if I could find it, was unable to repair it, erase it or reformat it). I replaced the Hard Drive, and the new one also failed in an identical way. The good news: We're not alone, and there IS an inexpensive fix for this. Dozens and dozens of others have experienced almost identical behavior. — check out the user stories at the bottom of iFixit's MBP 13" Mid-2009/2010 Hard Drive Cable page, as well as this iFixit forum — in addition to this forum on Apple Discussions, as well as this one. The consensus is that it's NOT the hard drive, but turns out to be the Hard Drive Cable (Apple Part #922-9062), for these units, which seems to have a reputation for failing. IMHO I would suggest that DIY'rs do the most important test first: Remove the drive and see if it functions — either in another unit or as an external drive, with a SATA to USB interface or similar. If it does, then erasing the hard drive and/or reformatting it will not only prove ineffective, but unnecessary. Just replace the hard drive cable (in my case it was this one) and you should be all set.