Virus/Worm 'not a valid Win32 application'

My system is infected with serious virus problem. My friend just gave his usb drive to add some movies. After connecting the usb there was tons of virus detected on the same. I am getting a constant not valid win32 application error on my screen. I was using a free edition of AVG before which looks to not working well. I bought Norton 360 here. But when I try to install I am getting same error on the screen. I contacted the customer support of my pc manufacturer who told me to install KB893803 update. But the installation is giving the same error. What should I do.

It looks your system is screwed up completely. The only way left is to format your pc completely and then getting rid of those viruses. It will be very complicated to restore your existing system. But still if you want to try you can go ahead with following steps. Boot in safe mode and scan your pc with good antivirus. This will be give you temporary relief only. Use CCleaner to wipe out additional files of your pc. If nothing works then just clean format your system.