azadeh
You are using an old method which is not recommended.
Use the Image Analysis window, and it will calculate NDVI instantly. If you must save the resulting image as a *.tif file on disk, right click in catalog and "Export".
For NDWI you need a short wave infrared band, which apparently you do not have, so this calculation is impossible. If I am wrong and you have another band captured in the short wave infrared, you can use the NDVI calculation in the Image Analysis window.
Cody B