It depends on what kind of listbox you are using. ActiveX control or did you just go to Data > Validation? if you are using an activeX listbox you can do this, but a Data Validation List has to be limited to one column.
If using ActiveX, the easiest thing to do will be to select the range of data you want to be included. Then name the range. Something like Range1 or something that you'll remember.
Then, insert your listbox from the developer tab, set the column count to 24 (since you have 24 columns you want included), and then type the name you gave to the range into the 'ListFillRange' field. The values should display.
HOWEVER, if at all possible I would highly recommend moving all your data for the list into one column. It makes things much easier. Making a listbox that requires 24 columns is a crazy amount of info to plug into it.