On a HP ProBook 4420s my wireless connection stopped working after some updates.

I looked in /var/log/boot.msg and saw no trace of the wireless driver being loaded.
So I looked in /var/log/boot.omsg and saw:

 [ 11.224842] iwlagn: Intel(R) Wireless WiFi Link AGN driver for Linux, 1.3.27kds
 [ 11.226111] iwlagn: Copyright(c) 2003-2009 Intel Corporation
 [ 11.227383] iwlagn 0000:43:00.0: PCI INT A -> GSI 19 (level, low) -> IRQ 19
 [ 11.228632] iwlagn 0000:43:00.0: setting latency timer to 64
 [ 11.228668] iwlagn 0000:43:00.0: Detected Intel Wireless WiFi Link 6000 Series 2x2 AGN REV=0x74
 [ 11.256845] iwlagn 0000:43:00.0: Tunable channels: 13 802.11bg, 24 802.11a channels
 [ 11.258146] alloc irq_desc for 36 on node -1
 [ 11.258147] alloc kstat_irqs on node -1
 [ 11.258165] iwlagn 0000:43:00.0: irq 36 for MSI/MSI-X

Then I decided to check:

# locate iwlagn

Some of the results included relevent modules files:

 /lib/firmware/iwlwifi-6000-4.ucode
 /lib/modules/2.6.32.12-0.7-pae/kernel/drivers/net/wireless/iwlwifi
 /lib/modules/2.6.32.12-0.7-pae/kernel/drivers/net/wireless/iwlwifi/iwl3945.ko
 /lib/modules/2.6.32.12-0.7-pae/kernel/drivers/net/wireless/iwlwifi/iwlagn.ko
 /lib/modules/2.6.32.12-0.7-pae/kernel/drivers/net/wireless/iwlwifi/iwlcore.ko

I found (after trying to manually modprobe the modules) I was getting this error in dmesg:

# dmesg

[ 1181.314606] iwlcore: Unknown parameter `led_mode'

Googling the error led me here:
http://centos.org/modules/newbb/viewtopic.php?topic_id=30883&forum=39
So then I investigated and realized I had to go to:

/etc/modprobe.d/50-hp-preload-led.conf

and comment out the line with

#options iwlcore led_mode=1

This is basically because the driver does not support that option. If you run:

modinfo -F parm iwlagn

the led_mode parameter is not there.

Hope this helps.

PS: The package that did this to me was sled11-branding-hp-bnb-1-0.116.1.