Try using the Windows Installer CleanUp Utility or Revo Uninstaller.
I've used those when i cant uninstall a program because it cant find the uninstall file or because i interrupted the install process.
Download the Windows Installer CleanUp Utility -
http://download.microsoft.com/download/e/9/d/e9d80355-7ab4-45b8-80e8-983a48d5e1bd/msicuu2.exe

Locate and run msicuu2.exe to install the Windows Installer CleanUp Utility.
Locate and launch the Windows Installer CleanUp Utility on the Start menu.
From the Windows Installer CleanUp Utility window, locate the application in the list and click the Remove button.
Once the application has been removed, click the Exit button to close the utility.

alunjah wrote:Some time if I install an application program on my system, the Task Manager is disabled
What cases it to act like so?

That has happened to me a couple of times before. To make a long story short, it all came down to my computer having a virus from programs i download from torrents sites or some unreliable source. Check your pc for any virus; i would recommend HiJackthis, and Spybot Search and Destroy. Thats what i used when i had that problem, last time being recently. Now i use a virtual machine to test any program im iffy with before i install it in any of my pc's.