login troubles (nonexistent user)

Hello everyone.
I have a question.
I’m having troubles with the log in in WordPress. I moved my site from my old server to a new one. So I exported the database to the new host with phpMyadmin, ad installed WordPress. After I did this all I couldn’t log in WordPress anymore by using my username and password. It says that the username doesn’t exist.
Not importing the database would allow me to log in, but then I would lose all contents and posts posted previously on the site, which I don’t want to happen, because I need to keep the old material posts.
I read the guide and I did everything written in there in the section about log in troubles except for Edit Users Table (it won’t let me click on Browse, the icon is grey), but however the problem is still there. Can anyone tell me what to do to be able to log in and solve the problem?

This is the information you might need about my system:

PHP Version 5.3.2-2

System
Linux w-09.th.seeweb.it 2.6.32-5-amd64 #1 SMP Sat Oct 30 14:18:21 UTC 2010 x86_64
Build Date
Jul 19 2010 01:19:53
Server API
CGI/FastCGI
Virtual Directory Support
disabled
Configuration File (php.ini) Path
/etc/php5/cgi
Loaded Configuration File
/etc/php5/cgi/php.ini
Scan this dir for additional .ini files
/etc/php5/cgi/conf.d
Additional .ini files parsed
/etc/php5/cgi/conf.d/gd.ini, /etc/php5/cgi/conf.d/mysql.ini, /etc/php5/cgi/conf.d/mysqli.ini, /etc/php5/cgi/conf.d/pdo.ini, /etc/php5/cgi/conf.d/pdo_mysql.ini, /etc/php5/cgi/conf.d/pdo_sqlite.ini, /etc/php5/cgi/conf.d/xmlrpc.ini, /etc/php5/cgi/conf.d/xsl.ini
PHP API
20090626
PHP Extension
20090626
Zend Extension
220090626
Zend Extension Build
API220090626,NTS
PHP Extension Build
API20090626,NTS
Debug Build
no
Thread Safety
disabled
Zend Memory Manager
enabled
Zend Multibyte Support
disabled
IPv6 Support
enabled
Registered PHP Streams
https, ftps, compress.zlib, compress.bzip2, php, file, glob, data, http, ftp, phar, zip
Registered Stream Socket Transports
tcp, udp, unix, udg, ssl, sslv3, sslv2, tls
Registered Stream Filters
zlib.*, bzip2.*, convert.iconv.*, string.rot13, string.toupper, string.tolower, string.strip_tags, convert.*, consumed, dechunk

MySQL client: 4.0.24
OS: Windows 7
Browser: Google Chrome
Wordpress 3.0.4 (Italian)

Thank you.