How can I reinstall Mac OS X (Lion) without erasing data?

My Lion installation ruined. Everything doesn't work. Even my Mac doesn't sleep. I want to reinstall whole OS, but I have no spare backup drive. So I want to reinstall OS without erasing or repartitioning to keep my data on disk.

I know it's not clear enough, but it should be a lot better than my current installation. So I want to try anything if it keep my data without backup.

Is this possible? How can I do this?

Or is there any way to repair current installation?

Solution 1:

Reboot your Mac. When you hear the boot chime, hold the COMMAND + R keys. You will enter the Lion Recovery environment. From there, simply choose to reinstall Lion. It will simply remove the current system and replace it with a fresh copy. None of your data will be deleted or moved. The only thing that will be replaced will be the core system files. There is no longer any need to make backups, migrate your data, or mess with partitioning.

If you'd like to read more about the Lion Recovery function, go here: http://support.apple.com/kb/HT4718