i have downloaded a few mp4 files yesterday using idm. when i clik to open the file ,my system freezes. earlier i used to open these kind of files without any problem. recently downloaded files have an unknown filetype icon. usually i get the vlc cone type icon ,. but now i get something like a chessboard unknown fileype icon. when in the explorer also when i click on any of the downloaded files, the system freezes. at that time i am not able to get the task manager also on pressing control alt del buttons. it takes a long time to recover from the doziness. when i made a system scan the avg antivirus says no threat. kindly help.