I recently created 2 small partitions, and after that, I shutdown my Mac. Then when I turned Mac back on today it took awhile to boot and then showed a blocked symbol.
I tried booting into the recovery partition. Then I deleted the partition, which is 10 GB in size, but I'm not able to delete the second partition, which is 15 GB. Also, when I tried creating the partitions before, it showed "Operation failed".
After some time, two partitions showed up, both named -- and greyed out. Macintosh HD no longer shows up in Disk Utility. Only some weird disk image shows up as OS X Base System.
I tried to reinstall macOS Sierra but the Macintosh HD partition again does not show up. I tried First Aid but it shows Macintosh is corrupted and needs to be recovered in Recovery, but I booted in the recovery partition only.
So how do I make my mac boot up normally and delete the 15GB partition without losing any data and erasing my HD.
macOS Sierra 10.12.5
And is this problem a serious issue or not?
gpt -r show disk0 per klanomath's request:
start size index contents 0 1 PMBR 1 1 Pri GPT header 2 32 Pri GPT table 34 6 40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B 409640 205318496 2 GPT part - 53746F72-6167-11AA-AA11-00306543ECAC 205728136 1269536 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC 206997672 29718320 4 GPT part - 48465300-0000-11AA-AA11-00306543ECAC 236715992 262151 236978143 32 Sec GPT table 236978175 1 Sec GPT header