E68: Hard Drive Error - It could be a problem with the Hard Drive itself or a problem with the internal connection to the hard drive, Try removing the hard drive and playing without it. Also this can be caused by a problem with the fans that make them draw too much power, it can also be caused if you have unnecessary accessories attached to the console like an external fan unit. Attempt to remove unnecessary accessories first, and then necessary components such as the hard drive and USB devices. If you have any case mods you may want to investigate those as well.
If the console works with the hard drive out, then you might want to invest in a new one.
Hope this helped