2 Answers

Two things you could try:

1) Your pickup rollers are dirty/worn:
Remove the tray, you should see either in the front or back some rubber rollers that feed the paper into the machine. These are much like tires in that they need thread to move the paper - if they're worn out, they need replacing - if they have a lot of paper dust or other stuff on them try to clean them with a moist lint-free rag. (Water only is fine, rubbing alcohol if they're bad)
Also look for a seperation pad, this will be a rubber or cork pad under the rollers. Clean this as well and if it's worn, replace.

2) A sensor is stuck or malfunctioning:
Run a page, make a mental note of where it stopped. Run another, did it stop in the EXACT same place both times?
Look in front of where the paper stopped, is there a small plastic flag right before the paper? Is it damaged or stuck? Try taking some canned air to that flag/sensor and try again.

Usually situations like these are either just simply worn/dirty rollers not feeding paper to the sensors in time or the sensors are damaged.
If neither of these resolve the problem then you may be looking at a solenoid issue or something else you wouldn't be able to repair on your own.

Open the access panel usually located in the back and make sure you do not have a paper jam.