Only one speaker works in my panasonic music system

Contact the authorized service center for Panasonic.

Either the speaker is bad or the source for audio going to it is dead.

... whatever that tells us.

If you severely modified the load to the amp by running more speakers than it's designed to drive and/or at a lower impedence, well, are you surprised?

It only pushes around 25 watts/channel AT TEN PERCENT DISTORTION through a carefully and unrealistically limited bandwidth specification.

http://audio.manualsonline.com/manuals/mfg/panasonic/sc-pm193_1.html?idRes=699618

Running 'clean' (under, say, 1% distortion throughout th 20-20000hz range) it probably only pushes 10 watts/channel. Once an amp is taxed beyond it's clean abilities it will start to distort, badly, and distortion will kill speakers and maybe the amp itself.

Register and download the manual for free at retrevo.com

http://www.retrevo.com/search?q=panasonic+SA-PT750

See "Play Mode" on Page 17

This would indicate a CD/DVD Changer Error.
The system thinks there is a stuck disc or other wierd problem with the CD/DVD changer.
Unfortunately these issues are rather hard to fix, due to the way the changers work.
Opening these units isn't that hard, however fixing an issue with the changer is very difficult and is best left for a specialist.
You may need to contact a local Panasonic repairer to get this one fixed.
Use the link below (if you are in the US) and enter your model number and ZIP code to locate your nearest repairer.
http://www2.panasonic.com/consumer-electronics/support/?cm_sp=Homepage%20Support-_-Header%20Support-_-Support%20For%20Customers%20Link
Best of luck, and sorry that I could not be of much more help than this.

Sounds like it's just in 2 channel stereo mode, only 2 speakers working out of 5 and a sub, look for a selector switch for switching to 5.1 surround, as far as the no video problem try replacing the cable for the video connection. 

Hi, I have a Panasonic SA-ak25 system. I played one cd then inserted a second. When the second cd had finished it ejected but the first cd is still in the player, When i try to eject it the lights start to flash and it always stops on no (4) can anybody help. Bob.

check your speaker polarity and recheck all pos and neg grounds