Q: iCloud for Windows is not signing in, just waiting endlessly after 'Sign In' button pressed

Symptoms:

• 'Sign in' button gets disabled
• Wait indicator is rolling beside the disabled button
• On 'Cancel' it closes the window and after it's opened again, all fields are cleared
• If left unattended, even for a day, it's just doing this 'waiting to something happen' state...
• No error message given or such.

Things to mention:

• Net is working (I'm writing this, right?)
• My credentials are not misspelled or anything (I could login here, right?)
  • If wrong credentials are entered, I have the proper error messages
• I have already uninstalled and re-installed, but the symptoms are the same
• iTunes is working right with my iPhone on this same PC
• OS is Win 7 with all mandatory patches installed