What cleaning solution do I use for a Yamaha recorder

Sounds like it might not be cleaned enough. They may have done the pots but the internal circuit boards may not have been done enough.

According to the manufacturer, the reset procedure is documented here and on page 42 of the instruction manual:
http://faq.yamaha.com/us/en/article/musical-instruments/keyboards/digitalkeyboards/portable_keyboards/psr500/656/2085/psr500-psr500m_factory_reset_procedure

Turn OFF the Power.

Press and hold the 'Custom' [RECORD/END] and [CLEAR] buttons.

Turn ON the power. The screen will display 'clr'.

Release the 'Custom' [RECORD/END] and [CLEAR] buttons.

Try skipping track one and start on track two. Trk 1 circuit might. Defect

Make sure that in the control panel of Windows, "Sounds and Devices" under the "voice and recording" tab, the Yamaha mixer is shown as the device for both voice recording and playback.

Unfortunately, I do not have a solution for you. However, I recommend calling Yamaha, as they should be able to help you troubleshoot the problem.

You could record short "samples" to be used in building new voices, however, it does NOT appear that you can record a vocal song with the PSR9000. The Tyros II and III have the capability to record vocals but the PSR9000 and Tyros I do not..

When playing back an arrangement, you can re-sing the song and have the vocal harmonizer track the arrangement.

You need to have a basic recording program installed on your computer. If you use Apple you can use garageband. If you use Windows you can install audacity http://sourceforge.net/projects/audacity/
You will have to install the drivers of our yamaha keyboard than connect it with the usb cable to your computer and select the PSR S710 as an input in your recording program.

If you only have a stereo output from the DT you need to record audio to a sequencer track so you can remix it better.

Is there possibly a write protect or lockout feature?

We're talking about audio recording. If so you must conntect your piano by using the L + R outputs with your sound card or mixer line inputs (that's how I do this). USB is ok if you want to use your piano as a master keyboard (MIDI). Another important thing is that you must have an additional application installed called sequencer ( for example Cubase Sx, Sonar...) which will let you store your digital music. I'm not talking about the proper settings of them because it could take a day or so...:)
Overall, you will have to learn a bit about the home studio, home recording techniques. There are tons of informations on web. A great thing is that you can use your CP33 as a master keyboard to control additional virtual instruments (VST) or for example play different piano samples (check Synthogy Ivory). Possibilites are endless!

Regards
Radek