In an empty data frame add the excel files using the Add XY data tool from arctoolbox, then you need to define the coordinate system of the data using the Define Projection tool (Probably a Geographic Coordinate System WGS84 if from a GPS or maybe one with a NAD83 data for North America).
Longitude is X and Latitude is Y and your data looks correct, BUT ensure that there are absolutely no records that are empty or incomplete and that your longitudes are indeed all negative... one little positive value and you are going to have a mess.
When you have successfully got all the data in the data frame, then introduce other layers as you see fit.
Worry about the other stuff when you have your excel data into a geodatabase with a defined coordinate system (or shapefiles with similar definitions). You other data may be in a projected coordinate system, hence, the mess when you try to add undefined data to a dataframe with a different defined coordinate system.