Uh need some computer help over here 'sai'

It's about sai, you see as i meantioned before im having like serius issues with my pc so, i've been trying to fix up and everything

but there seems to be a problem I can't really resolve...
While I was trying to dowload a program called ISO so it could read a file I needed for school work, for a starange reason, paint tool sai on my programs bar changed the icon to this:  Fortunelly I just had to replace the sai file gain on the bar by removing it and put it there again. 
Now here's the problem, when i open the file that had all my .sai files they had that icon. I then tried to open it with the program sai to see if it would change the icon back to normal .sai but my computer seems to not recognize sai as an appopriate program and doesn't open and so i clicked on other programs to see what happens and now they're all like this and I can't change it back I even tried restauring the file it self but nothing.
The files still open if I open by opening my sai and go "open" and I can still work with the files properly, but this icon really bothers me and i would rather prefer to have my old .sai icon

Can someone please help me? Even if you don't know how this kind of things work is there anyone you know that can help me please?

I use Windows 7 64-bit

Really need help ;A;,
Kitty