There are a couple of things you can check as a blank screen 
is not very helpful:

- verify that there are no actual error displayed (show html 
source)
- check the webserver error log
- which web server do you use? From where?
-try to load the extension from the cli (cmd line)

There are a couple of things you can check as a blank screen 
is not very helpful:

- verify that there are no actual error displayed (show html 
source)
- check the webserver error log
- which web server do you use? From where?
-try to load the extension from the cli (cmd line)

- verify that there are no actual error displayed (show html 
source:
   * absolute blank
- check the webserver error log
   * nothing
- which web server do you use? From where?
   * Apache/2.2.17 (Win32) mod_ssl/2.2.17 OpenSSL/0.9.8o 
PHP/5.3.6 mod_geoip/1.2.5v6
    Apache Lounge VC9 version (like you recommended me)
-try to load the extension from the cli (cmd line)
   * it also loads (and gives outputs)

I tried to compile myself and gives a lot of warnings:
C:\php-sdk\php53dev\vc9\x86\php-5.3.6>nmake

Microsoft (R) Program Maintenance Utility Version 
9.00.21022.08
Copyright (C) Microsoft Corporation.  All rights reserved.

Recreating build dirs
apc.c
ext\APC-3.1.9\apc.c(257) : warning C4244: '=' : conversion 
from 'apc_ino_t' to '
_ino_t', possible loss of data
apc_bin.c
apc_cache.c
ext\APC-3.1.9\apc_cache.c(657) : warning C4047: 'function' : 
'int' differs in le
vels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(657) : warning C4024: 
'apc_fcntl_unlock' : different t
ypes for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(666) : warning C4047: 'function' : 
'int' differs in le
vels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(666) : warning C4024: 
'apc_fcntl_unlock' : different t
ypes for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(679) : warning C4047: 'function' : 
'int' differs in le
vels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(679) : warning C4024: 
'apc_fcntl_unlock' : different t
ypes for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(687) : warning C4047: 'function' : 
'int' differs in le
vels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(687) : warning C4024: 
'apc_fcntl_unlock' : different t
ypes for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(733) : warning C4047: 'function' : 
'int' differs in le
vels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(733) : warning C4024: 
'apc_fcntl_unlock' : different t
ypes for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(743) : warning C4047: 'function' : 
'int' differs in le
vels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(743) : warning C4024: 
'apc_fcntl_unlock' : different t
ypes for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(750) : warning C4047: 'function' : 
'int' differs in le
vels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(750) : warning C4024: 
'apc_fcntl_unlock' : different t
ypes for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(784) : warning C4047: 'function' : 
'int' differs in le
vels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(784) : warning C4024: 
'apc_fcntl_unlock' : different t
ypes for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(789) : warning C4047: 'function' : 
'int' differs in le
vels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(789) : warning C4024: 
'apc_fcntl_unlock' : different t
ypes for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(1249) : warning C4047: 'function' 
: 'int' differs in l
evels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(1249) : warning C4024: 
'apc_fcntl_unlock' : different
types for formal and actual parameter 1
ext\APC-3.1.9\apc_cache.c(1310) : warning C4047: 'function' 
: 'int' differs in l
evels of indirection from 'int *'
ext\APC-3.1.9\apc_cache.c(1310) : warning C4024: 
'apc_fcntl_unlock' : different
types for formal and actual parameter 1
apc_compile.c
apc_debug.c
apc_fcntl_win32.c
apc_iterator.c
apc_main.c
apc_pool.c
apc_rfc1867.c
apc_shm.c
apc_sma.c
ext\APC-3.1.9\apc_sma.c(696) : warning C4047: 'function' : 
'int' differs in leve
ls of indirection from 'int *'
ext\APC-3.1.9\apc_sma.c(696) : warning C4024: 
'apc_fcntl_unlock' : different typ
es for formal and actual parameter 1
apc_stack.c
apc_string.c
apc_zend.c
php_apc.c
   Creating library Release_TS\php5ts.lib and object 
Release_TS\php5ts.exp
        rc /n /fo Release_TS\php_apc.dll.res /d 
FILE_DESCRIPTION="\"php_apc.dll\
"" /d FILE_NAME="\"php_apc.dll\"" /d 
URL="\"http://www.php.net\"" /d INTERNAL_NA
ME="\"APC extension\"" /d THANKS_GUYS="\"\"" 
win32\build\template.rc
Microsoft (R) Windows (R) Resource Compiler Version 
6.1.6723.1
Copyright (C) Microsoft Corporation.  All rights reserved.

   Creating library Release_TS\php_apc.lib and object 
Release_TS\php_apc.exp
EXT apc build complete
SAPI sapili build complete

My first test was with these binaries:
http://dev.freshsite.pl/php-accelerators/apc.html

Thanks
Ricardo

The warnings are fine and does not affect the runtime.

but it gives this output on phpinfo():

HTML:
( ! ) Fatal error: Unknown: apc_fcntl_unlock failed errno:6 
in Unknown on line 0

PHP error log:
PHP Fatal error:  Unknown: apc_fcntl_unlock failed errno:6 
in Unknown on line 0

ah that's already something better (but not related to the 
warnings).

Which binary do you use and where did you fetch it?

Can you try using:
php_apc-3.1.8-dev-+igbinary-1.1.2-dev-5.3-ts-vc9-x86.zip

php_apc-3.1.8-dev+igbinary-1.1.2-dev-20110321-5.3-ts-vc9-
x86.zip

from http://www.php.net/~pierre/ please?

Pierre, I had the same fot both your DLL as 3.1.9: total 
blank.

Thanks for your attention
Ricardo

Sorry but be sure that you actually use the right ones and you 
restarted your server.

We do use these DLLs on many various configurations and they 
work just fine.

I had restarted my web server. I switch between eA, Xcache 
and 
APC (3.1.6) without any problem. So, only these versions are 
with something that is not 100%. Can you provide APC 3.1.9 
binaries compiled by you?

Remember that the PHP works , only CI app is not in my 
tests.

Do you have Code Igniter (or other big framework) on your 
test bench?

APC is no longer supported in favor of opcache that comes bundled with PHP, if you wish to use the user cache, then look at PECL/APCu.