Acto,
This seems weird.
Try this.
Press and hold down <CTRL> <ALT> and press <DEL>
This should bring up task manager.
Close everything using End Task apart from Explorer and Systray.
Some applications may take a couple of attempts to close and you may get the message "Program not responding" or "waiting for windows close dialogue box to appear". Ignore these and click end task.
Now go to My Computer > Tools > Folder Options
Click on The "File Types" Tab
Do you see a picture and BMP?
If you do. Problem solved, hit change and associate the file with your choice of editing application.
If not then
Good Luck