Help , cant open :(

Hai, er i just downloaded CF[awesome game,heard from friend] i played it afew times at his house and i decided to download it today ^^. the surprising thing is, when i click start,A hgw watcher thing pops up and then another popup with the title of:
HGWC:the picture is an X . it says File is changed: W[2007] L[5] CShell.dll. then my avg pops up and say virus alert . what do i do??? reinstall? or?

Regards,
Ansel