The power on/off button on the remote control works but the channel & volume buttons no longer work

you can start with opening the remote control and clean the buttons on your remote control. don't use any aceton based products. there can be some grease on the buttons.
if you used the on/off and volume more then the other buttons.

Hello
It will be best for you to buy its original remote control. Universal remotes may also work with it, but some functions may not work properly. You can buy it from the Authorised Service Center for Toshiba at your town. Just give them the exact model number of you TV set [which can be noted at its back side]. They will give you the exact original one.

RCA RCR 311B model universal remote have setup codes for Toshiba. You may also try this remote. The codes are:
1047, 1071, 1103, 1105, 1108, 1159, 1163, 1178, 1188, 1190, 1191, 1196, 1211
I strongly advice you to buy its original one. OK.

OK, YES you CAN turn on the TV without the remote, in fact you can do nearly everything that can be done on your remote, on the TV itself, NOW look, CAREFULLY around the edged or sides of your set, you will find there are "Buttons" usually there are 6 - 7 Buttons, if you look carefully at them you will see they are marked, usually with a Volume Up & Down, word, or symbol, A Channel Up & Down, buttons a Menu, an Enter, and an ON/OFF button, & sometimes others. Now To turn on, Press and hold the Power button, the TV will Turn ON, you can change Channels, with the Channels, and Volume, with the Volume ones. The Menu button, will allow selection to all the other sub menus and settings. IF you need to get a remote, Please, get an original, it may be more hassle, it may take longer to get, it maybe costs more... BUT IT WILL WORK. Universal remotes, well, read through a few posts dealing with them, and you will see what I mean. IF you MUST get one, absolutely ensure that it performs every function the original one did, or you can have many headaches.

technically we call it debouncing it causes due to the faulty microprocessor in remote also it can happen due to faulty carbon contacts of remote below buttons.the solution to this is to replace remote but before that do one thing 70% THIS WORKS open ur remote then take a dry cloth & clean the surface below buttons if u r lucky then remote will be OK

Try to replace the remote control with a new one. If it doesn't work, then there is something wrong with your TV.

check to be sure your remote is sending IR signal, with
a smart phone camera hold remote IR eye in front of camera and click any buttons on remote, you should see
a light coming from IR eye. If no light emitting, remote needs to be replaced.

Hold down the MENU button on the control panel for more than 8 seconds to unlock buttons.
Lone99star

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/jason_77a19afa8d604dee

Is the front funtion button works in the TV the it could be a bad remote controller(the button switch inside) :)

I do know about this machine but as a general thing with electronic items :-
With the item turned off press and hold its power on button for 3 to 5 seconds before release or that in combination with either a channel change or volume button, so say power+channel up or power+channel down etc I can only hope this overides the lock out, other than that its say two buttons on a remote etc but this I do not know.

Hope this helps you.......