Computer not booting after hard drive discoect

I have four drives in my computer

• 500 GB HDD ext4 for data
• 2 TB HDD ntfs for data
• 250 GB SSD with debian linux
• 128 GB SSD with windows7

I have windows installed first and later installed debian on the other drive.

Grub contains a seperate boot record for windows7

Yesterday I discoected all drives to work on anothee driver. After recoecting my drives I can't boot at all.

It seems like the debian boot option got lost.

Booting from the debian SSD results in an error that asks me to insert a proper boot media.

Booting from the windows SSD seems to work first but resets with a blue screen while booting.

How can I restore the boot record? I don't want to reinstall everything!