What is telling you it is a virus if it is not detected?
Could just be a faulty installation of the os.
If you wanna check if it is a virus, run a full system scan with Avast, set it thorough and let it scan archives. Also run 2 online scans. Let us know if something is found.
It was not there 4 days ago and taskmanager works after the pc boots
It attacks after a considerable amount of time
All the above functionalities work at the time of boot but not after the boot
As u suggested i did run the avast boot time scanner n detected a trojen in my exporer.exe and untill now it has not affected yet . So i am hoping it was that trogen but i just wanted to know the name to get more information abt it
Click on the link in my signature and follow all steps there to make sure your system is clean. Instead of running the scan with Avast do it with two online scanners. Let’s see if we can find something. Also post a HijackThis log here and let me have a look.