My 2011 Macbook Pro won't start - folder with blinking '?' My Mac will not start up. I went to recovery mode and made a backup of everything on an external drive. Now the Mac only starts up from the external drive.

I have OS X 10.10, Yosemite. I tried to backup and restore but it failed.

Most of the time my internal hard disk is not mounted. I ran Disk Utility today and got the following message for my HD Error: Partition Map check failed because no slices were found

How can I fix my Mac and make it start without the external drive?
Looks like a disk problem, dying.
In the Recovery Partition (start while holding CMD+R), start DiskUtility do Repair Disk.
Even when the issue is gone after that, prepare to have the disk replaced.