im trying to follow those steps, but i cant install it again!!
Sounds like the file type associations in windows was changed. If the problem is confined to a few file types, then you can change them in folder options in the control panel. If all files are affected the best thing to do would be to do a system restore to a date prior to the problem occurring. Then you can uninstall any BB software and do a fresh install of the DM.
There is only one file needed to install and run DM. You may be thinking of the two different DM download files, one with out media manager and one with media manager.