Hi Md Hoda,
If BitLocker keeps asking for the recovery key every time you restart, the first thing you should check is the TPM status.
BitLocker relies on the TPM (Trusted Platform Module) to authenticate your system. If Windows can’t communicate with the TPM, it will trigger recovery mode.
To check it, press Win + R, type tpm.msc, and hit Enter. Make sure the TPM is Present, Initialized, and Ready.
If it’s Disabled, you’ll need to re-enable it in the BIOS/UEFI. Just restart your PC, enter BIOS/UEFI (usually by pressing F2, Del, or Esc), find the TPM/PTT/Security Device settings, enable it, save the changes, and reboot.
Don't hesitate to ask if you have more questions!