I poured 3 liters of water in expansion tank

[PanMaxon]

Hi to every one. New kid on the block.
I have a volvo 940 1998 celebration.
A few days ago 25/08/18. I had to top up with water the expansion tank. On daily basis morning and after work. but this time it drunk 3 litres of water and when try to start the red block M90 B230FK engine. just as abut to start it krkrrkk the engine suddenly stop. I had the inpresion it was battery. Try to jump start but no luck bla bla bla

The old engineer Gentleman who try to help opened the oil cap and whola it look like some one pured milk in it. saem on the dipstick.

My question is that head gasket or could be something else?

Ps I live in isle of man and not many volvo like my it could be the only one Please don't tell me to take it to the mechanic i have seen them how they work. { It will do} the motto over here

Thank you