Search for files using "My computer" and then drag and drop them on the message attachment window.

cannot find way to search for files on computer to attach to message on the message pane

I hope, I understood your problem.

I assume, that you want to create a new message with an attachement, right ?

If so, press 'F7' in the new-message editor, press the button for adding an attachment, you'll see an file-browser window opening,

where you can select the files on your disk.

thank you,