KERNEL PANIC

Hi there,

Gout troubles with my external drives. Lacie d2 USB 3 Thunderbolt series ( each 3 Tb) on my Imac 27" medio 2011. Yosemite is completely up to date. Until a few days ago everything was working just fine. ( I use the thunderbolt connection ) But then ... as always I dragged my external drives to trash ( to switch them off for saving electricity ;-) )... I switched them off ... KERNEL PANIC. If drives are on, they work perfectly. When I shut them off... kernel panic. Yesterday a friend came by with his brand-new Macbook Pro and so we attached the drives to his computer. Guess what? Same problem. How do I solve this? Luckily I've got a backup on my Time Capsule of all my data but the Time Capsule is 2 Tb large and I'm not so far away of more data.

Thanx for thinking about it. Hope I can solve this.