Can not install any application

[Otilio]

I am using HP desktop PC. I upgraded my operating system from Windows XP to Windows Vista. Now I am unable to install any program. When I try to install some application, installation wizard hangs and it gives me a error message saying that "internal error: Failed to expand constant "userappdata". You have any solution on that.

[Devasis]

It may be happen due config.nt file become corrupted. You have to make changes in file= line. For that you have to follow certain steps-
1. Open notepad ( start> programs > accessories > notepad)
2. Open %systemroot%/system32/config.nt
3. Check at the bottom the line
file=40
4 If file=20$%THY means file is corrupted and you have made changes in number which is after = sign.
5. Save the file and reboot the system.

[Solomon]

Please check that DEP or Data Execution Prevention option is on or not. When it is on you can not install any application. To check that just right click on my computer and click on properties then under the advanced tab click on performance. After that click on data execution prevention tab and make sure that it is only selected for windows programs and service not for all programs. I think it will help you.

[MrChris-]

Check that you have administrator privilages or not.The permissions under the following registry need to be reset:

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionSetup.

To reset permission use following steps-
1. Run regedt32
2. Navigate to the key
3. Click on Security and then Permissions and make sure the following accounts have the correct permissions:
Administrators | Full Control | This key and subkeys
Power Users | Full Control | This key and subkeys
System | Full Control | This key and subkeys
Users | Read | This key and subkeys