Only 2 speakers work and the woofer...and i cant open your manual for the schematic

Internal fuse. Or fuse near the speaker connections.

Remove power. Remove back cover look for
125v clear or ceramic fuse.

125V 5x20mm Fast-Acting Glass Fuse

Certainly any large speaker itself cant be used with
very weak computer out signal
The signal should have power amplification in addition to
voltage amplification to energise large speakers

bad capacitor

Alright i had a chance to look over things, this is how you are going to hook up the sub. first we'll be connecting the surround sound unit to the sub woofer.
surround sound unit sub woofer
left front: positive (+) <-----to------------->(+) left speaker level in
negative ( - )<- - -to- - - - - - ->( - ) left speaker level in

right front: positive (+) <-----to------------->(+) right speaker level in
negative ( - )<- - -to- - - - - - >( - ) right speaker level in

now that the surround sound unit is connected to the sub woofer you will need to connect the front surround sound speakers to the sub woofer.
sub woofer front surround sound speaker
left speaker level out (+)<-----to--------> (+) left front speaker
left speaker level out( - ) <- - - to- - - - ->( - ) left front speaker

right speaker level out (+)<-----to--------> (+) right front speaker
right speaker level out( - ) <- - - to- - - ->( - ) right front speaker

Alright now that the wires are all over the place and plugged in
turn everything on and see how it sounds. let me know if everything is working as it should. if you need help with anything else or if something does not seem right please feel free to contact me via e-mail or phone
Mark Woodring

nothing is wrong with the woofer the connect is broken at the strain relief and the cable needs to be replaced.
You can replace the connector if you know the pinouts. You will need the connector and the schematic.
you may be able to find the pin outs configuration here.
http://pinouts.ru/
As for the connector this may take a search online.

the conductor xxx\blk is the minus or black( from speaker) the outher is positive\red pin from speaker) the woofer is bigest speaker inside is connected on the crossover at low output, tweeter at high output, if you connect wrong you can burn speakers and crossover, you can test with very low volume on amplifier.

1st connect low to woofer, it only her low freq below 500Hz like drums and bass, if connect on med out the speaker is working as handpocket old radio audio. if connect on high the speaker is like no audio out. (the woofer take about 60-75% of amp power).

2nd connect the midrange at mid output you can listen to human voice cristal clear. if connect on high output you listem like esteric female shouting.

And connect the tweeter at the empty output

Take particular attention on polarity terminals, if you exchange the polarity you have a moofle sound traped inside of speaker, and some structered box noise who may open the box panels in future.

If you can open the cabinet of your woofer box please check all the wires connected to the woofer and use a multimeter to check the continuity of woofer coil.If shows no continuity replace the woofer

sounds like the voice coil could be open or damaged. the woofer can be reconed. reconing replaces all the moving parts in the speaker frame returning to new condition in most cases.
[email protected]

Plug red and white cables into woofer ports that are red/white
Plug purple lead into front of woofer to input port
green goes into accessory (green) port on back of computer
elbow shaped 2 prong leads go to speakers in back
DC power goes into front of woofer marked DC input

The output of the transformer goes to a RS404L bridge Rectifier. the 4700uF cap are leaking. Did you work in this area?