No sound output when I plug in the damper peddle. Casio cdp135. Any suggestions about what is wrong?

https://www.amazon.com/casio-keyboard-sustain-pedal/s?page=4&rh=i%3Aaps%2Ck%3Acasio%20keyboard%20sustain%20pedal

Yes. But it depends which connectors you have on your laptop. If you have a small (3.5mm) stereo jack input, then you need one cable with a small stereo 3.5mm jack on one side and a big stereo 6,3mm jack on the other side. (Take a look at the picture below).
Then you plug in side with a small stereo jack in your laptop "line in" input and other side of the cable with a big stereo jack to your Casio CTK-1100 Phones/Output plug on a keyboards rear side...

Be sure to adjust the volume on both the Casio (output volume) and laptop (input volume)...

Cheers!

PX 410r uses IDES 4.0 downloadable from
http://www.casio-europe.com/euro/emi/specials/ides/downloads/
and not another version.

I suggest you uninstall the Casio USB driver from Control Panel'system'device manager then Reboot the PC without the USB cable.
Download latest USB driver from :-
http://support.casio.com/en/support/download.php?cid=008&pid=20
64 or 32 bits versions are both available.
Load driver first. Plug in the usb cable only when software tells you to do so.
Uninstall Data manager if wrong version.
Install IDES 4.0

The output of the casio may only be mono, you can buy splitters to create a 2x channel output. Is there any other outputs from the casio other than headphones, usually there are red/white RCA outputs (Phono's) which would be better for connecting to your soundcard.

Hope I was of use to you, good luck.

If that is one of the ones with a plastic "hinge/spring", breakage is usually fatal... keep cord and plug for junk box.

Pat, the USB output on the Casio WK-210 is only capable of sending and receiving MIDI information. It's not sending any digital or analog audio. Audacity is primarily for sound file editing.

In order to use the keyboard to record onto your computer you can connect an audio cable from the 1/8" stereo mini-jack to an input on your computer. Then you can record into Audacity.

Or you can acquire MIDI recording software (ie. Logic, Cubase) and then using the USB output on the keyboard, you can control and record multiple MIDI instruments in those programs.

use the audio output to send the keyboards internal patch sounds, or use a usb midi adapter to use the keyboard to trigger the garageband midi sounds, if the keyboard has a midi output, that is. the usb output requires software drivers to use, and IS NOT mac compatible. You may have to select a midi source in garage band preferences or settings if you are using midi.

If I were to venture an educated guess I would vote for failing filter caps in the power supply.

The power is likely collapsing under load of the speakers but headphones take much less drive.

If this has an external wall-wart power supply, you might try a new one IF the output is found to be under the rated voltage.

Internal power supply components are beyond those individuals that are not adept at electronics.

Check that you don't have old batteries in the unit. Also that the auto power down is not activated.

If using a power adapter make sure it is the RIGHT one, both in polarity and current rating.

There are two types of damper pedal switches, on that is closed until you press it, and one that closes when your press it. It sounds like your Casio is expecting one type and your Roland pedal is the other type. A quick way to test this is to plug a guitar cable into the Casio pedal input and see if the keyboard sustains. If it does, then your Casio requires an "normally closed" switch.

Some pedals have a small switch near the cord or even on the bottom of the pedal that will reverse the switching operation (BOSS pedals, a division of Roland, have this feature). If you can find that, then change the switch position and you should be OK.

If not, and you feel like digging into your pedal, you could take the bottom off of the pedal and check out the switch itself. Many pedals use a switch that can be used either way. The clue will be on the switch itself. If there is an extra tab on the switch that is unused, then switch the wire that is furthest away from that tab to that tab. This will probably involve soldering, but it is nearly impossible to damage anything.
If moving the wire that is furthest away does not do anything, then try putting that wire back and switching the other one.

If your pedal does NOT have an extra tab, you're SOL, unless you want to buy a replacement switch (unsure of make). If this is the case, you are probably better off getting a different damper pedal - preferably one that is marketed as "universal"