Code:
pboxHangman.ImageLocation = "Images \ Hangman-  & numWrongGuesses & .png"
Anything inside of quotes is treated literally. So, given the following code:

Code:
Dim strMyMessage As String = "Hello!"
Dim intMyNumber As Integer = 1

MessageBox.Show("strMyMessage")
MessageBox.Show(strMyMessage)
MessageBox.Show("intMyNumber.ToString")
MessageBox.Show(intMyNumber.ToString)
Would pop up messages in the following order:

Code:
strMyMessage
Hello!
intMyNumber.ToString
1
From this, you can see that including a variable name inside of quotes does not result in the value stored in that variable to be used.

To demonstrate this, take the path you are trying to use to load an image from, and pop it into a MessageBox statement:

Code:
MessageBox.Show("Images \ Hangman-  & numWrongGuesses & .png")
You should see that what is displayed is probably not the intended path to one of your image files.