Virus infected my PC? Please help.

Hi,

I have a problem. Whenever i start my pc it opens up search window. whenever i dbl click on start menu or my computer or any folder/file to open it, the search window opens up again and again.
Also my task manager got disabled. I feel this is a virus. Please help me out.

Thanks in advance.

My OS is Windows Xp proffessional edition.Service pack 2