Using "if" and "validation" together - pick from one list, second list shows up

I was hoping that somebody could help me out on this.

I would like to have a validation table that, when used, provides a second validation table based on the selection made in the first one.

My company provides a wide array of services that I would like to divide into categories - the first drop-down would list these categories ("Cleaning", "Repair", etc.), and then have the next column's drop-down only show those services under the "Cleaning", "Repair", etc. categories.

I know how to make validation tables (I have already created the different tables, with each service under its proper category), but I don't know to get Excel to make one list "pop up" after making a selection from another one.

Thank you in advance.