Skype always crashes explorer.exe?

Two months ago I tried downloading Skype and it would never run. It always crashed windows explorer and I couldnt even end it through the task manager because explorer is frozen. The only way to get out of it is to turn off my computer.
I uninstalled it that time. But now I just got it again. And the same problem is still happening.
Whats wrong?
I'm on Windows 7 Ultimate 64 bit.