Skipping channels Every time I turn the tv on, it keeps skipping channels and won't stop. I've checked the remote's batteries and made sure the keys on the tv aren't jammed.

The first step is to make sure you have good batteries in the remote. The ones included tends to be cheap and you have no idea how old they are.
Here is the manual, page 12 explains how to use the remote and the next few pages cover the initial setup and scanning of channels.
http://www.mytoshiba.com.au/file/download/resource/file/23089/39al900a%20owner's%20manual.pdf

If the remote is still not working, get a universal remote to replace it. This link gets you the codes to program the universal to work with your TV. http://codesforuniversalremotes.com/universal-remote-control-codes-toshiba-tvs/

Can you please check the CH+ CH- keys if any of them stuck.

check your batteries to make sure they are good. if they are good you may need to default the remote and reprogram. if this doesn't fix it you will need another one

Check the remote control for its infrared emission. Check it with fresh batteries. Check it by pressing all the keys. You can detect the presence of infra-red emission from the remote control, using a cell-phone camera. If you wish to get more details about how to check a remote control, please visit this site. One among the posts has details about it. In some cases, the remote control might need to clean.
http://electronicshelponline.blogspot.com/
http://remotesearch.blogspot.com/
Search the site by type in this key phrase "how to test a remote control "in the "search box at the top right of the display window of the Homepage" to get the related post quickly.
https://youtu.be/wUpnETSm6_k
https://www.youtube.com/watch?v=jsSCNCW3IbQ [open and clean]
https://www.youtube.com/watch?v=Qp-l1uh-5gE [open and clean]

Dear Sir:
Follow this step:
Turn on the TV and grab the remote. In most cases, you will need the original remote to unlock the TV if you aren't sure of the unlock code. If you don't have the original remote, you will need to purchase one.

2 Look at the screen. If you see a blank screen with a red key on the bottom of the screen, press 'Function' and 'Mute' at the same time. This should unlock the channel. This is an option for people who want the TV to stay locked but, want to be able to bypass the lock to watch a certain show or channel. All other channels will remain locked and the TV will fully lock when it is turned off.

God bless you

Buy a remote control that have setup codes For Technica TV.

Be sure your remote hasn't got a button stuck down which is changing channels. If not, take the batteries out of the remote. If this stops the channel changing there is probably some conductve material stuck across the circuit board
inside the remote. If this is the case you have to check inside the remote by openning it up.

Problem with channel skipping has rectified itself. I simply unplugged the set and and started over with remote intructions on signal and channel setting. The tv was also turning itself off and on, this also has ceased. Thanks, hope I don't need you later.

Make sure there is no other remote control working simultaneously or with a key pressed constantly by mistake. In my case i found the air conditioning remote control with one key being pressed by my furniture next to my bed, it was causing that erratic behavior. As soon i realized, i stopped that remote control and problem solved. I hope this works.

ok, let's try the simplest things first.... unplug the tv from the wall, and remove the batteries from the remote. wait about 5 or 10 minutes. reinstall the batteries and plug the tv back in. try it again. actually since you said you tried another remote, you can skip removing the batteries from the remote. if it still does it, try unplugging the tv overnight. if it still doesn't work right then, you have a processor problem, and need to have it looked at by a service tech.