How to format the internal SSD, Please Help!

Please help

I have a 2015 MacBook 12” retina that boots only halfway, then turns off.

I have tried almost everything with 0 results. To make a long story short I see the SSD in Disk Utility, but, if I try to format it for a clean install it just hangs there for several hours without any result. It is formatted with APFS for the moment.

• I tried with terminal but I get the message that I have not permissions to format it.
• I tried with external USB with both High Sierra and Sierra and no result.
• I have tried to install from the net with Mojave Beta but I get the message that my disk is locked ….

Going really crazy now!!

I can see how much of my space disk is occupied 180 GB of 512 GB. When I click on info for the disk in Disk utility it tells me that my disk is NOT writable … hmmm I am lost

Please help

My knowledge in terminal is really basic so any advanced users are really welcome .

I really hate the soldered SSD’s , what idiot at Apple got that brilliant idea ???

Thanks in advance to any tips!

Best regards from Switzerland