Password

You should be able to get into the box using "linux single" from the boot prompt.

From what you wrote, I assume that you ARE getting a login prompt (if you boot the system all the way up), but you are not able to log in with any account.

Depending on what happened when you installed your network card, you may have accidently clobbered files in /etc. From your description, the most likely is /etc/passwd.

If you can get into single user mode, take a look at /etc/passwd (using more, NOT vi or linuxconf), and carefully examine the file for format errors. If you have a known good copy from before your user changes and card install, compare the two manually. Look especially for garbage near the top of the file. As with any debugging operation, you are looking for "What changed?"

In the unlikely-but-possible category, check the system date. If you have passwords able to time out, a wrong system date could lock you out.

Good luck.

Beside using "linux single" from the boot prompt, more serious problems can be recovered by using the RH installation CD. When booting up from the CD, type "linux rescue". This will force bootup from the linux OS. From here, you can try and do recovery by manually editing your files.

use some password cracker software available in net . mention the passwd file it will crack password

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