Well, being unable to open the task manager usually point in direction of a virus......
When you say "since I've installed LW", do you mean installed and downloaded things......??
Where did you get your version of LW from ??
In any case I reckon you checking your system using any of these programs (I reckon using all of them):
http://www.lavasoftusa.com/software/adaware/(free) http://www.grisoft.com(good free AVG) http://www.ewido.com(>>now called AVG Anti Spyware<< free 30 day trial -the best in my opinion) http://www.ccleaner.com/download/(free) Spybot - Search & Destroy (FREE)
If you can't get rid of it go here and get some free computer help:
http://norbiesworld.co.uk/computerhelp 