When I try to print the triangle with an exclamation point flashes and doesn't print

This is the 'Attention' light. It indicates that the cartridge door is open, or that other errors exist.

Not great info, but you need to methodically eliminate the possible causes of the error....

1. Try putting some paper into the Manual feed tray / slot. It may be waiting for you to feed paper manually. Check your printer driver settings....

2. Press the 'Go' button. It will make it print from Tray2

3. Check your Printer driver settings, and 'Page set up' in the application

4. Switch the device off, and unplug the data cable.

5.Switch it back on.

6. Print a configuration page from the printer control panel by pressing the Go button (the green one) until the green Ready and Error light start blinking.

7. If it prints these pages successfully, then the problem may be elsewhere (PC software, application, corrupt data, etc) but check the settings on the Configuration page as well.
Make sure they match your system, paper size and type, feeding options etc....