A couple simple tests you can do. Try removing one of your spark plugs, attach the wire, ground the plug against the cylinder head and try to crank. Look for spark. Replace plug and remove a fuel injector. Position it so you can see if there is any fuel being delivered when cranking. If both these tests fail, the HES is probably bad. It is a pain to remove, but there are plenty of videos out there.
Used motronics are available on ebay for much, much less than the $2700-2800 new price from BMW. If you have some jumper wires, disconnect the HES plug and run jumper wires to each terminal. Hook a volt meter set to 12V DC to the power and ground terminals and crank. If no reading on the volt meter, the motronic is fried. Once it is removed, you can smell if it is burned. It is a hideous odor.