I have hp pavilion dv4 laptop . The wif...

Your laptop goes into power save mode once the power suppply is disconnected. WIFI consumes a large amount of power so the system shuts it down to save power. You can disable it by going into control panel and power options. There you can change the power settings to allow wifi to run when using battery.

Hi I think I no the solution. In some laptops when you switch to the battery it disables the wi-fi after a period of time - this is entering power saving mode.

(Do this while on the battery power)
Go into your power options in the control panel. There you will see power save, balanced and performance. which every plan you choose go to settings and you will see the wifi options.

As for your device manager freezing make sure you are up to date with all vista updates by tpying into the search box "windows updates". Also recently there was a service pack released for vista make sure that is installed as there are some hot fixes!!

At the time when laptop is charging, go to power settings and disable the battery (energy) saving option, as this option starts to switch off devices one by one to prolong the discharge time.