Have been using ubuntu 10.10 with complete wifi access but recently when I upgraded it to 11.04 it shows no wifi.Please help.

Make sure you have the relevant driver for your dongle/wifi card. Also make sure that the card manufacturer has driver support for your distro. You can usually find out on the manufacturers website.

Here are some helpful pointers:

With your computer turned off, insert your wireless adapter into a suitable port/slot.
Turn on your computer and log-in if/when prompted.
Open a terminal window and enter the following command:
This program will output the information Network Manager has collected about your card, much of which will assist in setting-up wireless networking .
If the output contains:
State: connected
(and you are not on a wired connection) then your wireless adpater is working and connected to a network.
Left-click on the panel applet (four vertical bars in 9.10 or older; 4 concentric arcs in 10.04). If you can see wireless networks, then your wireless works; you need to connect to a network. See below on network connection.
1.3. Troubleshooting Steps
Troubleshooting wireless networks in Ubuntu can be approached in three steps in order:

Check that your wireless adapter is enabled and that Ubuntu recognizes it: see Device Recognition and Operation.
Check if drivers are available for your wireless adapter; install them and check them: see Device Drivers.
Check your connection to the Internet: see Wireless Connections.
If it still does not work, ask a question at Launchpad, Ubuntu's official help: instructions.
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