After changing the drive letter I get the error Inaccessible_boot_device?

At the beginning I just had the problem that my external hard drive was not recognized. After researching the net, I tried to change the drive letter of the hard drives. I did that and even changed it back again (the same letter as before). After a restart, my laptop can't boot. I receive the following message: "Inaccessible_.boot_device".

Resetting (without data loss) stops at 8%. Then do not continue.

The last recovery point is August (too far!). However, I only saved important data last week and absolutely need it.

Can you help me please?

Are you coming into the BIOS? What is there because of LW in it?