Hi,

after some months of using Windows 7 and some BIOS updates I updated to Windows 8. And today I updated the new BIOS. Unfortunately I was using BitLocker which never made some problems - until today. Now it is asking for the key - which I lost... So it's denying

Well my bad. But I want to try, to install the old BIOS. Is this possible to downgrade and where can I get the old version?

I think all you need to do is suspend BitLocker, then enable it again.

I guess now it's too late?

I think the suspend and re-enablement helps refresh the key storage so I would do that anyway.  It won't hurt.  Just don't turn BitLocker off then back on.  That's a full decrypt then re-encrypt.

But since I locked my system partition as well, I can't boot. So where should I suspend BitLocker :-/
Thanks for your help anyway :)

This is going to be one of those YMMV answers, so apologies ahead of time.

Similar problems on W510 going to the latest BIOS, found I had to go de-list HDD1 on the BIOS boot list.  Just the regular partition.  When you boot up with the storage key or typing it in, hopefully you get that far, I then entered Bitlocker in the windows search, launched it, found the C: drive and did a suspend, then a resume.  Then things seem to come back normally, but I also resaved the key on a USB key.  Good luck.