problem after software update

I've took delivery of my second M6SL after the first one became a paper weight. The problem is after upgrading the software to
M6SL_2.004.6, i get the "upgrading software please wait.." message then nothing. It just switches off, I've tried a soft reset a hard reset and it still has the same screen, I've tried waiting about 5 minutes before starting up and nothing. Now it won't connect to my mac or linux machine, i don't really wana use the dfu tools

any suggestions, before this one goes back

Read the FAQ carefully and thoroughly