php 5 doesn'find extensions

Hi all!

my configuration:
- OS: Windows XP
- server: IIS 5.1
- MySQL: 4.1.6 gamma-nt
- php 5.0.2

- installed php 5.0.2 from zip file
- configured C:\windows\php.ini, starting from php.ini-recommended, with
options:
extension_dir = "c:\php\ext" and
extension=php_mysql.dll

- set %PHPRC% = C:\windows
- added C:\php to %PATH%
- configured IIS for .php extension and C:\php\php5isapi.dll
- php libmysql.dll has been copied into C:\Windows\System32
- net-stopped/started IIS
- reset machine

Initially, php worked with MySQL and I executed some queries.
BUT, SUDDENLY, PHP STOPPED WORK:
- Appears the well-known message "PHP Startup: Unable to load dynamic
library 'C:\php\ext\php_mysql.dll' - Impossibile trovare la procedura
specificata.".
- When found, at the line "$connection=
mysql_connect($host,$user,$password);" procedure stops without ant other
message.

- I removed the whole php directory and repeated all installation (three
times), but now I get no message and procedure always stops at the line
"$connection= mysql_connect($host,$user,$password);"

- The problem isn't specific to Hi all!

OS: Windows XP
server: IIS 5.1
MySQL: 4.1.6 gamma-nt
php 5.0.2

- installed php 5.0.2 from zip file
- configured C:\windows\php.ini, starting from php.ini-recommended, with
options:
extension_dir = "c:\php\ext" and
extension=php_mysql.dll

- set %PHPRC% = C:\windows
- added C:\php to %PATH%
- configured IIS form .php extension and C:\php\php5isapi.dll
- libmysql.dll has been copied from c:\php into C:\Windows\System32
- net-stopped/started IIS
- reset machine

Initially, php worked with MySQL and I executed some queries.
BUT, SUDDENLY, PHP STOPPED WORK (I didn't changed any configuration):
- It appears the well-known message "PHP Startup: Unable to load dynamic
library 'C:\php\ext\php_mysql.dll' - Impossibile trovare la procedura
specificata.".
- When found, at the line "$connection=
mysql_connect($host,$user,$password);" procedure stops without ant other
message.

- I removed the whole php directory and repeated all installation (three
times), but now I get no message and procedure always stops at the line
"$connection= mysql_connect($host,$user,$password);"

- The problem is not specific to php_mysql.dll, but occurs with all
extensions (e.g. php_oci8.dll)
- MySQL installation has a different libMySQL.dll (1.044 kB instead of 228
kB): I tried to replace the php dll with this one, but it doesn't work.

I searched over many forum but I cannot find any suggestion.
Can someone help me?
Thanks!!!