It is a problem with the domain trust.
So I created a local account, login using the LOCAL account, and was able to start SQL on single mode and connect using CMD.
Thanks all for your support.
Glad we could help, and thanks for letting us know. (At least you should have the SA password now so you can get on to the server and look at/adjust things.)
PS: no idea how to solve that problem with the trust.
Your Windows Server/AD team will probably have to work on that, it is likely related to delegation and/or SPNs. It might end up being easier to join the server to the actual Domain you want, unless there is a reason for it to be different.