Good afternoon all.
I have a Mercedes Vito dualiner 2.1 diesel that has started just recently having starting problems.

Started around a month ago when I left the hazard warning lights on by mistake and parked up for a few hours. When I came back it was dead and I had to jump start it with a booster. Ran the engine for approximately 2 hours and turning off and on again seemed fine.

Next day it was dead again, jumpstarted it again and ran for a while and it seemed okay for the next week. Then the same happened again so I assumed it was the battery so bought new one.

All was okay for 2 weeks, then started it yesterday just to move it a few feet on the driveway, turned off and went to go out an hour later and again it was dead.
Jumpstarted it again and ran for an hour and after turning it off it started first time every time (4-5 times)
I checked the starter fuse and battery cables were secure to make sure.

Today, again it is dead.
The dash lights come on but it doesn't even try to turn over when the key is turned, just a single click and nothing at all.
Yet if I get it started and it runs for a while then turn it off it starts again after first turn.
It seems if it's left overnight it goes again???
Is this going to be an alternator? Starter motor? Solenoid? Faulty battery?
Thanks for and any answers.