Enable your mysql extension in php.ini (and be sure to modify the right one).

where can i enable it?
in this part?

[MySQL]
; Allow or prevent persistent links.
mysql.allow_persistent = On

; Maximum number of persistent links.  -1 means no limit.
mysql.max_persistent = -1

; Maximum number of links (persistent + non-persistent).  -1 means no limit.
mysql.max_links = -1

; Default port number for mysql_connect().  If unset, mysql_connect() will use
; the $MYSQL_TCP_PORT or the mysql-tcp entry in /etc/services or the
; compile-time value defined MYSQL_PORT (in that order).  Win32 will only look
; at MYSQL_PORT.
mysql.default_port =

; Default socket name for local MySQL connects.  If empty, uses the built-in
; MySQL defaults.
mysql.default_socket =

; Default host for mysql_connect() (doesn't apply in safe mode).
mysql.default_host =

; Default user for mysql_connect() (doesn't apply in safe mode).
mysql.default_user =

; Default password for mysql_connect() (doesn't apply in safe mode).
; Note that this is generally a *bad* idea to store passwords in this file.
; *Any* user with PHP access can run 'echo get_cfg_var("mysql.default_password")
; and reveal this password!  And of course, any users with read access to this
; file will be able to reveal the password as well.
mysql.default_password =

; Maximum time (in seconds) for connect timeout. -1 means no limit
mysql.connect_timeout = 60

; Trace mode. When trace_mode is active (=On), warnings for table/index scans and
; SQL-Errors will be displayed.
mysql.trace_mode = Off