problems with ads

Good day to everyone

 

i have a problem with a virus or whatever it is

 

2 kinds of ads pop up in a browser window (not in another window, but in the  body of the current page. i can drag it and drop anywhere else within a page)

ad contents are constantly changing

 

Безымянный1.JPG

 

Безымянный2.JPG

 

i'm afraid i don't know where i could fetch it, cause i was preparing for my exams and was surfing many unreliable pages.

i've downloaded many .doc files in archives, but scanned each with norton

 

i'm using internet explorer 6 and Windows XP sp2

3 full scans with my Norton Internet Security made no result and found anything

it says than system is clean

 

how can i solve this problem?(

 

Thanks