Boot from Linux CD with ntchpw utility installed. Most of the time I used PING. Pretty sure most of Live CD’s do have that utility.

Mount Windows partition to Linux:
ntfs-3g /dev/hda1 /mnt/ntfs
OR
mount -t ntfs-3g /dev/hda1 /mnt/ntfs -o force
The last one is used if windows did not shut down properly.
In Windows partition Navigate to WINDOWS/system32/config
Execute chntpw SAM. As a safety measure you can copy SAM file somewhere available to restore, if things go wrong.
This utility will ask you number of options. Blank the password, do not set a new one. Agree to write hive files when finish.
Restart computer to boot into Windows.

By default chntpw is loading administrator account. You can load another user if required. Read man page for chntpw to figure out how to do this.

Here is the problem: Vista is connected through wired or wireless connection to a router. IP assigned, no error messages in the connection. Pings are going too Google and updates are downloaded from Microsoft. Probably can go online in messenger or ICQ. But when you start up Firefox or IE, it does not let you go surfing the net.
When you boot Windows into Safe Mode with Network it can go browsing with no problem.
The solution in my particular case was to remove Norton Anti-virus suite. Just when I uninstalled it everything worked fine. Did not even need to reboot.

Start cmd as Administrator. To check MTU issue:
netsh interface ipv4 show subinterfaces
This will give you a list of network adapters with MTU

To change the MTU issue following
netsh interface ipv4 set subinterface "YYY" mtu=xxxx store=persistent

Where “YYY” is a network interface name like “Wireless Network Connection”.

After uninstalling Vista SP1 you may get the yellow triangle error for
the wan miniport (SSTP). You can’t uninstall wan miniport (SSTP) or
delete it.

This is the solution:
Use the following commands to be carried out as the user Administrator
(Run as Administrator) from Command prompt (cmd):
netcfg -e -u ms_sstpminiport

You may have to find the course Hardware ID device from the Device
Manager and selecting the Details tab-> Hardware IDs if it is not
‘ms_sstpminiport’ which is causing the problem.

Taken from: Here

Vodafone VMC Lite does not want to connect to the network if if is executed under Windows XP user with restricted privileges. The software comes up, but saying “No device” and no chance to connect.

How to resolve this: Login as Administrator, Uninstall VMC Lite and install full featured VMC software from Vodafone. Connect to the network. Then login as user and try to connect again – it should work now.

Bear in mind that WinXP is treating every USB port available as separate instance, not connected to each other.. so being logged in as Administrator plug in USB modem to every available port and connect. Otherwise you’ll hear moans from users saying modem is not working.

Simple solution, but I’ve spent quite a time to figure out the way.
RIP Vodafone -)

Sometimes you need to remove device driver manual, because Device Manager in Windows does not want to remove anything and gives you “Error 31”.
If this is your case, this is the guide for you. I’ve spent a sleepless night trying to figure out how to fix this problem..
In my case that was Network Adapter Drivers that did not want to work. Wireless adapter did have a yellow triangle and in properties it showed Error 31. All the attempts to remove the device or driver did not work – the device just appeared again. So I had to manually remove the drivers.

Run device manager find your driver file and *.inf file are used by this device.
55577595
55577595

For driver files you have to read providers. If provider is Microsoft you can’t touch driver and
driver service – you can only remove non-system drivers

Remove registry folder:
HKLM\System\CurrentControlSet\Services\

Next remove driver files (*.dll,*.sys) ,*.inf file relate to your device you can find in

C:\Windows\inf\<inf_name>.inf
C:\Windows\inf\
<inf_name>.pnf
C:\Windows\system32\drivers\<driver_name>.sys
C:\Windows\System32\DriverStore\FileRepository\
<driver_name>

Don’t forget to do full backup of registry and not completely delete driver files, but misplace them: put in C:\tmp

Information taken from this discussion: http://www.vistaheads.com/forums/microsoft-public-windows-vista-general/440447-error-31-about-6t04-wifi-adapter.html