I am using Windows vista. every thing just works fine when i log in to my primary account that is administrator but when i switch to some other account on the same computer my yahoo messenger does not works properly i can log into my yahoo account but when i try to chat with my friends i cannot see any thing on the screen of chatting windows how to fix this problem

That happens when you are running a user account that is not the administrator account. In many ways this is smart because trojans and viruses have the same trouble installing. In schools or office buildings where they want to control who installs what on the computers it makes less problems for an administrator to fix. In your case switch users and log into your administrator account in control panel see if you can give your usual user account administrator privileges, shut down administrator account and log into your usual account and see if it now has administrator privileges in the control panel/user accounts. If not then install software while logged in the administrator account but install for all users from now on. Or you can only use the administrator account and set it up the way you like it (like your regular user account)

That happens when you are running a user account that is not the administrator account. In many ways this is smart because trojans and viruses have the same trouble installing. In schools or office buildings where they want to control who installs what on the computers it makes less problems for an administrator to fix. In your case switch users and log into your administrator account in control panel see if you can give your usual user account administrator privileges, shut down administrator account and log into your usual account and see if it now has administrator privileges in the control panel/user accounts. If not then install software while logged in the administrator account but install for all users from now on. Or you can only use the administrator account and set it up the way you like it (like your regular user account)

Microsoft's latest operating system, Windows 7, and its predecessor, Vista, offer a new layer of security that is different from previous releases, such as XP or 2000.
The earlier Windows versions treated all users as system administrators by default. With Windows Vista and 7, all accounts are treated as limited users.
The User Account Control utility provides elevated permissions when required and prompts users for those permissions.
You can control UAC behavior in Windows 7 so it does not prompt you for these permissions.
Start your computer with Windows 7 and log in as you normally would. Your desktop should appear, and any background applications should be closed.
Click the Windows "Start" orb at the lower left corner of your screen.
Click your account picture at the top right of the menu.
You will be presented with a window that allows you to make changes to your user account.
Click the link that says "Change User Account Control Settings."

Look for the User Account Control options slider.
The default option of User Account Control is to notify you only when programs try to make changes to your computer or you install new programs.
The option directly below that does the same thing but does not dim your desktop.
The "Never Notify" option at the bottom of the list eliminates the prompts for permissions.
Move the slider to the bottom of the options window.
Click "OK."
You may be prompted one last time from User Account Control to confirm your settings and reboot your computer.
or
Log in as an Administrator on Windows 7
If you've recently upgraded from Windows XP to Windows 7, you're probably wondering how to log in as an administrator. In Windows XP, the administrator account was clearly visible from the log-on page, but it's no longer there in Windows 7.
Although there is an administrator account, it must first be enabled with the Windows command prompt before you're able to use it. Enabling the administrator account lets you troubleshoot problems with programs on your computer.

Click on the "Start" button, and then type "command" into the search bar.
Right-click "Command Prompt" when the results appear.
Click "Run as Administrator."
The command prompt opens.

Type "net user administrator /active:yes," excluding the quotation marks.
Hit "Enter."
Click "Start," and then click "Switch User." Click the "Administrator" icon to log in.

If you have another account on your laptop that has administrator rights, log in into that account and change the password for your account. If you have an administrator account (even if you don't try putting in Administrator and leave password field blank) try using that account to reset the password, otherwise try one of the following:
- see this for XP http://support.microsoft.com/kb/321305
- or this for Vista/Win7 http://windows.microsoft.com/en-us/windows-vista/What-to-do-if-you-forget-your-Windows-password
- or if anything else didn't work you can use third party software from Hiren's Boot CD to reset your login password http://www.hirensbootcd.org/download.html

Login With the Administrator Account in Windows XP Professional

Click the "Start" menu and then click "Log Off."

Click "Switch User" when the prompt screen opens.

Press "Ctrl," "Alt" and "Delete."

Click on "Administrator" when the "Log on to Windows" screen pops up. Type in the administrator password, if applicable.

Click "OK." You will now be logged in as the administrator.

Log On as An Administrator in Windows Vista

Start your computer and allow it to continue through its startup process. By default your computer will simply load directly to the primary user account (usually the administrator account), but if there are multiple users on the system it will load to the account login screen.

Use the mouse to click on the administrator account from the list of available accounts to log on. This step is only necessary if you've customized Windows Vista with more than one account or you have set the operating system to load the login screen first.

Enter the password required in the password field to log on to the administrator account.

Click the "OK" or "Log On" button once you have entered the password. This button may be labeled differently depending on the version of Windows Vista or any GUI (graphical user interface) changes you may have made.
Log on as an administrator from within the Windows Vista environment by clicking on "Start" and then "Log Off." As soon as you have logged off, you will be returned to the login screen where you can choose the administrator account from the available list.

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Forgot Windows log in password

Forgetting your Windows administrator login password. With no way to get into the system, you can’t even perform basic maintenance, let alone a thorough tune-up. Formatting is always an option, but we consider that a last resort. (Plus, guess who’s going to have to help reinstall all the programs lost after a wipe?) But all hope is not lost. There are a few ways to actually retrieve a lost Windows account password. Read on, and we’ll show you the light.

1st Method:
The first thing which you check if you forget login password. When we install Windows, it automatically creates an account "Administrator" and sets its password to blank. So if you have forget your user account password then try this:
Start system and when you see Windows Welcome screen / Login screen, press ctrl+alt+del keys twice and it'll show Classic Login box. Now type "Administrator" (without quotes) in Username and leave Password field blank. Now press Enter and you should be able to log in Windows.
Now you can reset your account password from "Control Panel -> User Accounts".
Same thing can be done using Safe Mode. In Safe Mode Windows will show this in-built Administrator account in Login screen.

2th Method:
There are a lot of Windows password revealers and crackers available, but we’ve found that Windows Password Recovery Tool is the most effective.:
Windows Password Recovery Tool is one of the easiest password recovery tools to use. It allows you to reset a user account password, including the Administrator password. It is also a relatively small download.
Windows Password Recovery Tool Service: http://www.windowspasswordsrecovery.com

I resolved this problem by creating a new user account with administration rights. Logged on as the new user. Then logged off and logged back on using the user account that had problems and hey presto everything was working normally again. It seemed that in creating the new administration account windows repaired any corrupted files that was causing problems.

change the user account to administrator, to unlock privileges.
That should solve your problem, remember to restart the pc so changes are made in the registry

kind regards and please don't forget to rate us

Sounds like a virus......if all the trouble shooting you have done didnt work the only thing you have left is either take it to geeksquad or format the HD and reinstall windows.