Digital Compass

I found a stange problem yesterday when i want to rename any file. that is when i typed new name and press enter, it says-if u change file name extension, the file may become unusable. and then i have to select the file format every time i open it. the songs cannot b taken on to a mp3 cd also. i am not able to change d name of photos, downloaded things,etc. there is no virus. i dont know wt has happened....few days b4 my comp was operated by my cousin but he says he hasnt changed any settings.

After googling i got the way to correct this problem just go to tools-> folder options ->view and check "hide exensions for known fie types" . it probably fix your problem and if it cant then your system has a virus and it need Antivirus to be cleaned