In the right pane, scroll down to Shell. If the value (under the Data column) is not Explorer.exe, double click on Shell, type Explorer.exe in the Value Data field, and click "Ok".
Then expand HKEY_CLASSES_ROOT and click on .exe The values in the right pane for this key should be as follows:
(Default) = exefile
Content Type = application/x-msdownload
If they are not as I listed them, change them the same way as I suggested for the first key. Let me know what you find.