ican't login on my server

Common bootstrap choices:

• Pressing the C key during boot triggers a DVD boot and would generally require media having been created locally or an older (10.6.8 or earlier) bootable distro DVD from Apple, and a functional optical drive.
• ⌥ triggers a bootstrap chooser (used when there are multiple bootable disks present)
• ⌘R is a recovery boot.

If you're looking to reinstall and have the recovery partition, then ⌘R would be typical.

If you want to try that DVD, then the optical drive is a common failure and booting from an external USB DVD drive will usually work, whether it's an Apple SuperDrive or a third-party USB DVD drive.

If you don't have a recovery partition and don't have a USB DVD drive, then you'll either need to create a bootable partition on another disk or locate an installer, or use a FireWire (if this is a Mac Pro) or Thunderbolt connection and cable and another Mac to wipe and reinstall, or use an Internet network boot. You'd use FireWire if the system you're having trouble with is a Mac Pro. AFAIK, Mac Pro does not support the Internet network boot.

If you're comfortable using the command line, there's a way to create a USB installer using a command-line tool, and here's an example.

hi . did you already try reset the password just hold down command + s it will show the black screen

just follow the instruction below :

https://discussions.apple.com/docs/DOC-4931