When I start Mathematica 9, dialog with "Choose a MathLink program to launch" appears.When i cancel the dialog, Mathematica will stop. I've found that this could happen when Mathematica is used with own C++ programs, but I don't use it that way, I just want to start Mathematica. I tried to uninstall and remove specific directory as it is written here and install again with no success. What should I do?

EDIT:

When I cancel the dialog, this message dilog appears:

```
Serious startup error
Mathematica could not establish a connection to the kernel.
Kernel: System.
Low-level MathLink error: Unknown internal error.
```