Problem with file associations

[Slym]

Hello,

my problems started couple of days ago when I tried to open a damaged .avi file with BSP. The file could not be opened, BSP offered me to check for suitable codec but it couldn't find one. I let it go, after that I did the usual work on my computer, I didn't install anything except Echolink software. I turned off the computer, and after turning it on again I noticed that .avi files I had on desktop changed to WMP icon, but I didn't do anything about. Later, I wanted to play a movie, but it opened in WMP. I draged the file to BSP, but it showed me an error DirectShow not installed...

I tried to uninstall BSP, restart the computer and install it again, but that didn't help either.
After that, I researched and found out that the error appears in the case of corrupted quartz.dll file. Then I tried to install DirectX 11, but since I'm using Windows 7 it's already integrated, it wouldn't allow me to install it. Then I took quartz.dll from another laptop with Windows 7 I mange and copied it to system32 folder. Now I wouldn't get the error and BSP would play a file if I dragged it to it. After that I tried to install DirectX again, but I got another error, so I deleted the DirectX key in the registry wich tells it what version is installed. After that I did a chkdsk /r /x /b, sfc /scannow and cleaned up and defragmented the registry with Registry Mechanic. I installed DirectX and BSP, went to BSP file types, unchecked them all, closed BSP, restarted the computer, checked them all again but nothing happens. When I go to Open with... and browse to BSP .exe file, I click open but nothing happens and it doesn't show up on the list. The same happens if i try it through Default programs in Control panel. I "uninstalled" the WMP but that didn't hel in any way either...

I reall don't know what else to do and I'm hopeless