Q. i am trying to insert a page number, but when i do the running head disappears

Here are the steps for Word. Instructions are a little different for Office 365. If you are on a small scree, you may need to rotate your device to landscape mode to see all options in Word. 

1. Double click in the area in which your header will go at the top of the page.  
2. From the ribbon select the header pull down menu and select the Blank (Three columns) option.
3. You’ll put your title in column one, delete column 2.
4. Highlight column 3 and from the ribbon select current position> plain number.

You'll now have a title and page numbers for your running header. 

For Office 365: 

1. From the ribbon select insert> Header & Footer. 
2. By default the Blank (Three columns) option is you header. 
3. Put your title in column one, nothing in column 2.
4. In column 3 select Page Numbers from the ribbon and select the correct number position, with the number showing in the upper right corner. 

You can see more in our Tips for Formatting Your Paper in Word.