When I was mucking around yesterday booting Windows in "safe" mode, the Serial Port menu item became greyed out. Therefore I assume that the driver is not (fully) installed. Did you install the device driver as instructed?
You can directly edit the preferences.txt file (see the IDE preferences for its location). Once you have found the location, close the IDE, look for COM1 and change it to COM4. Save and restart the IDE.
However I found that even doing that did not help if the driver was not installed.