The most common reason for that message (about no program being associated with a file) is simply that you haven't got a relevant program on your PC. For example, if someone sends you an Excel spreadsheet you must have Excel (or a compatible program) on your PC, or you won't be able to open it.
You need to examine the file extension (e.g. .pps or .xls), to determine what type of file you've received, in order that you can install a suitable program (if one is available) onto your PC.
Here are a couple of common examples:
If the file extension is .xls, it's an Excel file. You need Excel (expensive) or Excel Viewer (free) to view it:
http://tinyurl.com/5rkr2b
If the file extension is .pps, it's a PowerPoint presentation. You need PowerPoint (expensive) or PowerPoint Viewer (free) to see it:
http://tinyurl.com/3buwr5
If your attachment has another file extension please post again, telling us what it is. Someone here will probably be able to point you towards appropriate software for opening the file.
Chris