software problem

i had avira antivirus and downloaded and installed pc scanner,it is a software,it corrupted all files of windows and all the other installed softwares such as internat explorer,mozilla fire fox,itunes,winamp,adobe flash,when ever i click open it shownig window either to install or to posses that the file harmful.please help me,to get way,im using windows7 ultimate.

realsitically all you can safely do is use a "live" CD such as one of the Linux distributions to back up your files, and then reload the machine using your windows setup disks
whatever you downloaded was obviously viral. Trying to solve it through the forum is not realistic. Wipe it and start again
I notice you are using Windows 7 Ultimate. It is rare to see that outside of businesses. Are you sure you ahve a legal copy of it? If not,and you have a bootleg disc, then that may also be virused

I would boot into safe mode first and use spyware removal software as well as your antivirus software to see if you can remove the problem.

You could also try running an online scan.

http://www.kaspersky.com/virusscanner
http://www.pandasecurity.com/homeusers/solutions/activescan/?

etc are just a few.

A backup and reinstall is probably required but its worth a shot first.

On another note, Windows 7 Ultimate is a retail version, windows 7 enterprise is used within a business.

Colin
my point is Windows 7 Ultimate is rarely seen except as bootleg. Especially in India