Loading files

If I double-click an XLW file, it starts up Excel but doesn't load the file but, if I use 'file/open', it works fine. This has just happened 'overnight' as it worked fine before.
Any suggestions, please?

I've solved the problem.
I searched some other forums and found 2 suggestions:
1) run excel /unregserver followed by
run excel /regserver from the start menu, or
2) in excel, goto tools|options|general & uncheck 'Ignore other applications'

The second option cured it.
I've put this solution in, incase anyone else gets the problem.