You can open your stingray filter up quite easily to investigate, assuming you have the filter turned off!
Start by removing the front cover by opening it as if you were changing the media and remove the motor/impeller by squeezing the two plastic clips and pushing the motor from behind it will slide out very easily.
On the bottom the impeller is easily viewable (white usually) and there is a small oval shaped cover you can easily remove that usually without much effort. Remove that and remove the impeller. Check the impeller does not have any debris stuck around it preventing it from spinning. To remove the top part of the motor you need to squeeze the two pins on side and after wrestling a bit the top part will "Slide" off.
Once you have it completely apart following those steps your best bet is to wash it under some running water. Remember you're only washing the motor not the filter media so there really should be no worry! Make sure you clear any gunk out that may be trapping the impeller from spinning properly ensure when you place it back it in can freely rotate (the magnet part now the plastic tip, the plastic blade/tip will only spin 180 degrees/ish) Place the bottom cover back on and blast some water down through the top outlet, clean the directional nozzle at the top under the tap water also. Then place it all back together reversing the steps above.
You can then test this in a bowl of water, get a big bowl fill it up with water ensuring your filter is all in one piece put it into the bowl of water plug it in. Turn it on, you will probably find it jets out quite powerfully. If this does not work your filter may well and truly be broken
If this works replace it back into the filter and ensure it is seated properly, place the filter back into the tank, the trick with the stingray is to submerge it and then rotate it whilst underwater to allow all the air bubbles to escape, turn the filter upside down in the water so the "Tail" part of the filter is pointing vertically you should of removed all the bubbles by now. Place the filter back onto where it was and turn it on.
If this all of a sudden stops working, I would give your 2 filter sponges a quick squeeze in some tank water. (Take a bowl of water out of your tank, put your filter sponges in them and give it 2/3 quick sharp squeezes you may find a lot of plant debris/poop is released place it back into the filter and try again. If for some reason again this does not work even though your filter works in the bowl... then... I'm lost!
EDIT
On all occasions that I have tried to use my Stingray filter it has failed miserably. First attempt the filter wouldn't seal properly and all the water was bypassing the sponges and the impeller gunked up pretty fast. Second attempt same again but it had sucked in so much sand tht the filter was non functional. Third attempt the filter finally closed properly and sealed! Unfortunately the directional nozzle was stuck and tore through my plants and my Amazon swords were somewhat damaged! I wrestled hard to fix it but the lid and seal issue is a big one, it seems to open ever so slight that you can even feel the water being sucked in through it!
On my girlfriends 60Litre tank we used a Fluval U2 filter instead, although you may get away with using a Fluval U1. I am probably going to purchase myself a Fluval U1 for my 40L tank to replace the Stingray. Although the Stingray is apparently more efficient at processing poop. Though the price tells me otherwise.
/i16.ebayimg.com/03/i/001/20/1e/1dbe_35.JPG, Mine however is white so I imagine there is a various amount of colours depending on what version it is.
