Sudden change of icons on desktop

I have a computer 32 bit, windows 7. Some icons on the desktop and at start have turned into PDF. I cannot even do a system restore as it has turned into PDF. However my word files are not affected. Program shortcuts such as Ashampoo Burning Studio, Microsoft word are affected. In fact the user cannot explain how this has happened. After having run MSE, no virus has been found. The only solution that i have found until now is to create another account for the user. However i would like to know what may have caused this problem and if there is a solution to it.

Please note that icons of word files have remained intact. Only shortcuts of programs are affected.

Thank you