I do not think it just died overnight.
I believe those people who worked on your car busted a fuel inlet hose causing the leak. When they tried to start the car it sucked in a lot of air.

If air gets between the Fuel Injection Pump and the Injectors in those Steel Tubings it compresses and does not want to move. Cranking the Engine to get the air out of this area takes a tole on the Battery and the Starter.

Another possibility is that after starting a car that sat a long time is that it loosened a lot of stuff in your Fuel Tank that has now plugged up your Fuel Tank Strainer (at the bottom inside of your Fuel Tank) or 1 or both of the Fuel Filters.

I am hope that you can give the Car a rest somewhere while you get a hold of some manuals so you will understand before you start tinkering.

Go up to the top of the page and put the cursor on the Resourses Button; you will see DIY Articles and DIY Links.
Click on either but read through both of them. Your 240D is similar enough to a 617 Engine as far as the Fuel System goes that you can use that information. Just disreguard the info concerning the Stuff that would go with a turboed engine.

__________________
84 300D, 82 Volvo 244Gl Diesel