After standing for a couple of weeks, i'm now greeted by a whole host of problems from my 94 540.

The car started and ran for 20 mins ok, but then there was a sudden 'heavy vibration' at any speed over 45 mph(ish). This went away after 10 miles or so, but has happened a couple of times since, again, going away after a short while.
Coming back I indicated right and was presented with a 'trans program' error. The car went into limp mode and I made it home.
After switching off, the car would not start again, not even attempt to turn over, nothing. The electrics seemed ok and working, and there was a faint electronic whirring sound which oscillated for about 10 seconds.
After about 15 mins, the engine started again, but if any lights or other electrics were turned on, the engine would idle erratically and the 'check control' message was displayed!

I cant believe that all these problems are independant of each other, so what could be the single point of cause of these problems?

TIA