Looking at your post I don't see enough detail to offer much else.
I have windows XP loaded in my desktop. This problem i am highlighting has started for the past few days only.
Whenever i try to load any software (By clicking the exe file) the installation wizard makes its appearance for few secs and then disappear. Again when i try to install the comp says "cannot install when already one installation is running". This is giving me problems as i am not able to load any software. The antivirus also doesnt show presence of any virus. Can anyone be of help to solve this problem