Siemens eq.6 switches off after brewing startup

Hello,
after days of browsing forums without finding anything, I now have to open a thread myself.

Siemens eq.6 plus s300 - E-No. TE653501DE/11 kept asking for descaling. I have descaled the machine several times in succession and now I have the following problem:
- switch on the coffee machine
- display symbols run/switch through
- ceramic valve buzzes and clicks several times
- pump starts, flushes water into drip tray
- brewing unit moves up
- machine switches off (display off) !!!

I hope that a coffee machine professional among the forum members here can help me. The machine is already a few years old, so it's out of warranty.
I've already removed the casing, but I don't know what else I can check. I also can't get into the service menu because the machine switches off immediately.

Thanks in advance for your help