I installed 12.04 and when I boot my computer, I connect to my WiFi and I put my password, all was good but in 2 seconds, it prompts me to enter a password. Internet works but for only 2 seconds, and not more.
Click on the Network Manager applet from the top panel, click on Edit Connections..., click on the Wireless tab.
Select your wireless connection name and click Edit. Click on the Wireless Security tab.
Enter you password, tick available to all users.