Problems like this are often caused by shell extensions , download and run this app:
http://www.nirsoft.net/utils/shexview.html
And then disable all entrys that are marked white and red and see if the problem is still there or not.
If it is gone , then eneble them again one by one to see wich is causing the problems.
PS, a entry marked red is very likely malware of some sort. If you have any marked in red then dont eneble them again and post wich they are back here please.