280se turns off on its own

From what you've provided your transmission could be seized which would choke your engine out, you could have a computer issue or more.

Before anyone can help you're going to have to give a bit more information:

• Is this vehicle a daily driver and it just started happening or a barn find?
• Are the vehicle fluids at the correct level and correct color?
• Is the parking brake engaged?
• Is your battery charged enough to maintain engine operation?
• Are you able to put the vehicle in gear?
• Is the engine idle erratic? ( surges or lack of fuel die off)
• Are there any weird noises?
• Have you looked under the vehicle to ensure there's no: transmission, drive housing, engine case damage; blockages preventing movement; weird smells?

If you could provide the steps you have taken, sounds you hear, smells you smell, and observations made as a list it would be helpful (and frustrating on your end I'm sure) to troubleshoot your vehicle.