Do you have additional information on fdisk /mbr?

The fdisk /mbr (master boot record) command is an undocumented switch used with the fdisk command (MS-DOS 5.0 and higher) that recreates the master boot record on a hard drive.

Does doing fdisk /mbr more than one-time have any effect on the computer?

How this command operates varies depending on the version of fdisk you are using. However, this command overwrites the information that is contained in the MBR. Performing this command multiple times does not do anything more than performing the same steps again.

Recreating the MBR on a different hard drive other than my primary hard drive

Use fdisk /cmbr <drive number> where <drive number> represents the drive you want to recreate the master boot record. To determine the drive number, run the fdisk /status command.