Windows editor

[Reverend]

Welcome to the board chem.
Unless anyone else know's a quicker way,i suggest you try this.

Open Windows Explorer.Go to Tools > folder options.Click on the file types tab.
There will be a long list of file types.Scroll through the list and find the ones you are having problems opening.Highlight them,(one at a time).Each time you highlight a file,if it's associated program has been changed you will see a restore button(bottom right).Click the restore button,then click apply.Continue through the list until all associations are back to default.

Hope that helps.

Update: if the "restore" button is not there,click the "change" button,and choose the appropriate program from the list that will appear in a new window.