Hi there, maybe this will help someone in the future:
I encountered the two-beep-black-screen issue this morning, googled happily for solution and found nothing, (this may be relevant the issue appeared after my mini fell on its side).
To the point: in my case it occured that the keyboard ribbon fell out of the socket, after I removed it completety just to see what it looks like under the keyboard and booted the mini a miracle happened
it didn't beep and went on booting normaly.
So if reseating the RAM doesn't work you may as well try the keyboard trick I followed the instructions from this very forum "Dell Mini 9 Disassembly Pictures".