The ID would likely be 'admin' for most DVR's or NVR's. The password would be either '4321' or '4321abcd'.
To hard reset the later SRD series, the only way to do so is to use the remote controller. Try pressing the buttons in the following sequence:
Freeze - Alarm - Freeze - Alarm - Freeze - Return
Try doing this a several times, with 10 seconds interval until it works, as the DVRs can be picky when it comes to accepting the signal from the remote controller.
If you are successful, you should see the pop-up message on the monitor screen, indicating you to choose a new password.
For the earlier generation SRD's, the method varies. You should refer to the manual, as the method should be stated, 100%.