Your question does not provide all the information necessary to absolutely resolve the issue. By now I suspect you've already resolved the issue or given up. Perhaps someone can use this info.
Need to know: Operating System (Windows 95/98/Vista/XP/7/8), Application (Word, Paint, Firefox, etc), type of job (jpg, pdf, text, etc.)
There is no short answer possible; but, I may be able to help with a generic answer. I can't help on Apple but I suspect it's the same as Windows, (and Unix, Linux, OS2, etc.).
Provided the Printer works proper on normal 8 ½ x 11 stock (print media) then it is not a printer or Queue issue unless it is just confused. As a printer technician I have seen this resolved by rebooting the machine(s) and trying to print again. If that doesn't resolve the issue you need to know:
The application you send the print job from tells the Queue what stock (letter, legal, card, envelope etc) to expect. The Queue, a component of all versions of Windows, is created when the printer is initially installed on the computer. The Queue holds print jobs and then sends them on to the printer when the printer tells the Queue it is ready. Some applications are more robust allowing more options than others. However, printing from inside a browser is frequently sketchy. If you're printing from an application that is different from the one that created it you may face an issue of the printer not getting the correct stock information.
: First before you attempt to send the print job check the settings in the app to insure your job has the right paper stock selected. Then, as you prepare to send the job from the app to the Queue before you hit the final "Print" button, check the "Paper Source/Size/Media" boxes in the "Printer Properties" to make sure your sending the right stock information. If that doesn't fix it; try to save your project in a format readable by another application and try to print it from the other app.
Note: 1. Print jobs are served to the printer by the Queue one at a time on a FIFO (First In First Out) basis. Sometimes print jobs get hung up in the Queue. A hung print job will block all subsequent jobs until the hung job is cleared. When a print job is sent and nothing happens (no printer activity or error messages on the screen.) look in the System Tray for a printer icon. Open it up and see if there are any jobs hung. If so cancel them and start afresh. This may require a reboot.
2. Print Queues can (rarely) become corrupt and must be deleted and rebuilt.
There are still variables too numerous to mention.
You can get HP Support at
HP Photosmart C7280 All in One Printer support
Whew! I've never tried to help resolve this issue in a post. Good Luck!