So right now what you have is saying:
If the textinput is blank AND if the attachments are blank then disable the control. What it sounds like you want is If the textinput is blank OR if the attachments are blank then disable the control. This is b/c you are requiring both.
In terms of logic:
the positive is TexInput2 AND Attachments
which means the opposite (or contrapositive) would be:
!Attachents OR !TextInput2
Since you are using the contrapositive version this would be your formula:
If(IsBlank(TextInput2) Or IsEmpty(DataCardValue14.Attachments), DisplayMode.Disabled, DisplayMode.Edit)
Not sure if the ';' should be ',' or not as that is based on your location/syntax used there. Hope this helps!