Suddenly not able to login

[Bilal Ghayad]

Dears;

Suddenly that is what I am getting (and I tried too many users without any luck);

[User@Machine /]# mysql -u user -p
Enter password:
ERROR 1045 (28000): Access denied for user 'user'@'localhost' (using password: YES)


[User@Machine /]# rpm -q mysql
mysql-5.0.88-1.fc10.i386
[User@Machine /]# rpm -q mysql-server
mysql-server-5.0.88-1.fc10.i386


Actually, I was not use the server for about 10 days, and then I restarted it. Then I am not able to login for the database. I do not know what is happening.

How I can resolve this?
I need to take backup from my database.

If we assumed that I do not have any solution, then how I can take backup? Currently I have the following:

[User@Machine mysql]# ls
ibdata1 ib_logfile0 ib_logfile1 billing mysql mysql.sock test

And I am caring for the billing database, so what I can do?

Regards
Bilal