Wot SD said.
I once did a wipe-and-reload. it took me weeks before everything was back in place. It went on the blink again soon after. Not doing that again!
Back up your important stuff, then do a "new installation". Ignore the first repair option it offers you (the one that's in geekspeak). When it says it's detected an existing installation and do you want it to use that, tell it yes. That's always fixed it for me.
If you think the hard drive might be dying, buy a new one (avoid Maxtor) and clone the old installation to that. Cloning tips are in here. Then remove the old HD and see if the new one will boot OK. If yes, you won. If no, repeat the "new installation" above.