Cant Install Mcafee Antivirus?

Ok this is what I did

-uninstalled ALL of ad awares files and buttons.

-ran ccleaner and reboted

-went throught a search in start menu and deleted all of what i had left of ad aware

-tried to reinstall ad aware then delete but ad aware wont install because it says ''ERROR 1721 Their is a problem with Windows Installer Package''

Mcafee Antivirus will not install because of ad adware. PLEASE HELP. I have got to many many sites. Someone tell me something right.

Cant Install Mcafee Antivirus?anti virus

The Windows Installer service manages the installation and removal of programs. The service applies a set of centrally defined setup rules during the installation process. These setup rules define the installation and configuration of the installed program. Windows Installer uses the Microsoft installation engine to install or remove programs. If the registration of the Microsoft installation engine is corrupted, you may not be able to remove programs that you have installed by using Windows Installer. In that case, you have to unregister and reregister the Windows Installer service. To do this, follow these steps:

1.Start your computer in Safe mode. To do this, follow these steps:

a. Restart the computer.

b. After the BIOS information is displayed, press F8.

c. Use the DOWN ARROW key to select Safe Mode, and then press ENTER.

d. Use the UP ARROW key and the DOWN ARROW key to select your computer, and then press ENTER.

2.Log on to the computer as local administrator.

3.Click Start, click Run, type cmd.exe, and then click OK.

4.At the command prompt, type msiexec /unregister , and then press ENTER.

5.At the command prompt, type msiexec /regserver, and then press ENTER.

6.At the command prompt, type exit, and then press ENTER to close the command prompt.

7.Remove the software program from Add or Remove Programs.