WIFI not working in Ubuntu, what to do??

If you have freshly installed Ubuntu and your WIFI is not working. Then you should follow the following steps to hopefully resolve the issue.

Goto System/Administration/Hardware drivers
See if any drivers are listed as to be installed or in-active.
In this case install the driver and enable it.
Restart the machine

Still not fixed
If you are using a Compaq machine in particular and also in general, sometimes the drivers are installed properly but the wireless button does not work. In that case, first check to see if it is disabled. If it is, then enable it

rfkill list all
# if blocked =yes then try next command
rfkill unblock all

If you still have problems then may be you have the BCM4312 802.11 b/g rev(01) card
Check to see if this is the case

lspci | grep 802

If in the output you see BCM4312 802.11 b/g rev(01)
then you should do the following

sudo su
apt-get update
apt-get install bcmwl-kernel-source
shutdown -r now

You would need to restart for the changes to be effective
If in case it still does not work, check in system/administration/hardware drivers. A LINUX STA driver will be listed. Click on install and then enable it in the same menu. After this reboot.
Everything should be working now! :)

Ubuntu network manager and disappering nm-applet icon

I had this strange issue with my Ubuntu install when the nm-applet icon a.k.a. network icon disappeared from the task bar. After much effort i found out a work around that was to stop network-manager application and then launch nm-applet and then restart the network-manager application.

But the solution to this is a very simple one, and as it turned out was not a bug.
If you are faced with such a situation do make sure to checkout your /etc/network/interfaces file to see that the interface is not listed. If the interface is listed in that file remove it else the network-manager wont take over that interface by default.

sudo service network-manager stop
nm-applet &
sudo service network-manager stop

Sample lines in /etc/network/interfaces

auto eth0
iface eth0 inet dhcp
auto eth1
iface eth1 inet static
address 192.168.244.2
netmask 255.255.255.0
gateway 192.168.244.244
 

Comment out the interface you want network manager to take over, in this case eth0

#auto eth0
#iface eth0 inet dhcp

auto eth1
iface eth1 inet static
address 192.168.244.2
netmask 255.255.255.0
gateway 192.168.244.244
 

Then you may simply restart your pc or you can simply restart the networking using

sudo /etc/init.d/networking restart