If your wireless network adapter was working fine then suddenly dropped or became unreliable there is a chance that it may have been a software driver update that made it stop working reliably. You may even have opted to download this driver yourself thinking that if it’s from Microsoft then it must be good, right?.
I seem to be seeing this more frequently on Vista than any other operating system. For this, I’ll presume that your problem is the new driver so you need to get back to the original driver and then disable any hardware driver updates within Windows Update so you don’t see this problem again.
To reinstall the old wireless network adapter software driver
Go to Device Manager then under network adapters right click the adapter and go to properties. Click the driver tab then click “Roll back driver”. When finished, restart the computer and you will hopefully get a stable wireless connection.
Note: If the “Roll back driver” box is greyed out then you do have another option. Open system restore and roll back your system to a day or so before you installed the driver. Bear in mind that this will make any program that you have installed since unusable until reinstalled. It’s also worth backing up your documents too as system restore is quite a critical task.
Driver updates are generally “opt-in” so you shouldn’t get this again. Make sure that you have only ‘Recommended updates’ turned on.