A few things to try,
Turn off the sub, remove the RCA cable from your receiver and place you finger across the pin and outer ring. Turn on the sub, it should turn on and create a really pissed off humming sound from your finger. You can tap across it with your finger to a good rythm you can dance to if you like. If it is still silent, turn off the sub and do this.
With the sub off, place your fingers around the cone of the sub and lightly press inward. Do you hear any scratching, crunchy sounds or is the cone "frozen" in position. If it is anything listed above--you roasted your subwoofer. If it moves back and forth quietly, generally speaking you should be OK unless the internal connection to the voice coil failed.
Most likely, if it just ups and dies one day--it is usually related to the amplifier or the output from the receiver. The "finger trick" usually works well enough to turn it on and make humming sounds if the receiver has a subwoofer out failure. You can also connect a 1/8th inch to dual RCA cable to your phone and wire it into the sub to see if it turns on and plays something (more accurate than your finger!) If it plays from your phone, your receiver output is toast. If it does nothing, you have an amplifier problem.
If your sub is ported, take a sniff at the port and try to get a wiff of burnt electronics--very distinctive. That is a very bad sign if it has the burnt smell and it might be something easier if it smell normal. IF it smells normal, unplug the thing for a few hours and remove the amp from the back of the box. Some of them have a cover over the amp module others don't--if you have a cover, remove it. Now look for burned up components, they tend to be black, smell bad etc. find any? No? Good! Look for fuses, some amps use components that don't look like fuses--because they don't want end users messing with them. Don't yell at the messenger! Now, if it smells good, no burned up parts--check for fuses. If you are really lucky, they might have a amp schematic online and you can look at it for fuses--they are generally labeled as F1, F2 and so on. If the schematic lists several of them, if you can't obviously see one--have a friend that does electronics look at the thing which will cost you a six pack of their favorite beer (just sayin')
Since you have the amp out, might as well throw an ohm meter across the subwoofer--expect to see anywhere from 3 to 8 ohms depending on the subwoofer design. If it is below 1 ohm--that usually means the voice coil is partially melted which can short the coils together which will drop the impedance and burn up the outputs of the amplifier. Not very common but it happens. Normally, since it abruptly stopped and you are in an apartment--generally the amp would be the most likely failure point. You can check to see if the two wires going to the sub are still connected because weird things happen.
If your amp has failed, you can either ask the company if they have spare amps (highly unlikely) or you can replace the amp with another plate amp of the same power and filtration (if required) Other options is to seal up the back of the sub, install some terminals like on the back of your speakers and program an outboard amplifier to be your new sub amp. You can use pro sound amps that have programmable limiters and DSP to get it correct. Cost for that?
You can get 100 watt plate amps from Parts Express on sale for $50 to $100 and PA amps with DSP start at around $350 so just quoting options. Since it is so old, rather small...the PA amp would be overkill but this is AVS!
No worries about your speakers "suddenly failing"... some of those speakers in malls have been playing annoying music for decades without failure. Generally speaking, they are quite reliable as long as you don't overdrive them, start them on fire etc. Speakers can last 20 to 50 years and usually just don't stop working out of the blue--no matter what teenagers say. Now if you overpower them or drive them with really low bass that the cones mechanically can't do--then you damage them that way. I doubt in an apartment you'll normally go into rockstar mode so..l. your mileage will vary.
Personally, I own three plate amps with one of them being 21 years old and the two others at 6 years old. Audio amplifiers fail also, I have an Onkyo make it 17 years, a Pioneer that was given to me that made it 33 years, a Carver amp made it 24 years and a very expensive amp blew the output tansistors 6 months out of warranty. It happens! The output transistor failure was coased by alien anal probes so Deaf Forever understands.
Sorry to hear of your sub troubles--that is what makes audio so much fun! You can either find out if a new amp is available, use a different plate amp or get a new subwoofer is generally your options. Good luck and may your next sub outlive you!