Will not tune in channels on auto store

Most likely it needs a converter box. To see for sure, just turn it on and look at the channel type.

1. Channels are displayed as decimals, such as 17.1, 17.2, 17.3, 18.1, 18.2, etc. In this case it's a digital TV which needs only an antenna. Also usually TVs like this display no signal as a blue or black screen, though sometimes they can have the fuzzy gray screen.

2. Channels are displayed only as single numbers, 1, 2, 3, 4, etc. Most likely the screen is gray and fuzzy, maybe making a loud fizzy noise, when you have no signal. It's an analog TV and you need a converter box.

You can't ADD any more channels than the TV comes with, eg CH00-CH99. :)
However, I gather that you mean you want to tune unused channels to a station.
The quick way is to go to your menu, tuning, auto-tune.
This finds any strong enough TV signal from lowest frequency to highest frequency, plus some which may be too weak/snowy too view.
Once auto-tune is complete, a program starts showing.
It's now up to you to edit Channel Settings to re-arrange or delete in preferred order. Some sets allow renaming from eg CH-4 to 'TV1' or whatever your choice. Usually max 5 chars.

Are you trying to pick up standard analog channels (the kinds that have a fuzzy gray screen when there's no signal)? Those stopped functioning in 2009 when the nation ended the analog broadcast. You can only get digital channels now, except for a low-power broadcast station here and there. Nowadays for analog, TVs mostly pick up only radio stations.

When you are auto tuning the system will not store a channel which is week by its standard ( at least 60% signal strength ) This done to avoid grainy picture and hissy sound.
You can go into manual tuning and store it.

Hello

You just do autotune to receive all channels. In this mode TV will tune through the entire channel band automatically, and finally will stop tuneing, and will show the first channel receved. You must be patient for these time. about two or three minutes, without disturbing is process. The tuning process follows.

Auto Tuner Setup

In Auto Tuner Setup, the TV automatically scans

t h rough all available channels, memorizing the active

ones and skipping over blank ones or channels with

weak signals. This means when you scan (using the

CH A N N E L +/- b u t t o n s ) you will receive only clear,
active channels
P ress the ME N U b u t t o n
Press UP or DOWN buttonTo AUTO TUNER SETUP
Press Right or Left button to operate
Press Vol+ or Vol (--) to choose CABLE or AIR
Press UP or DOWN button to move to START
Press Right or Left Button to start Auto Tuner Setup

Tv will show "NOW PROGAMMING" display.
Programming will take approximately 1 to 2 minutes.
After all it will show
PROGRAMMING OVER

Some cable systems experience interference from radio frequencies on cable Channel 95. You may delete this channel from
your scan by removing the "X" next to it on the Channel Summary screen.

Try manual tuning on that particular channel. if the transmission signal is week nothing can be done by the user.

Welcome to the world of off-the-air broadcasting!

First, be sure you have the TV set up correctly and that is in fact capable of digital tuning. Just because a set was sold as HDTV doesn't mean it has a digital tuner. Small TV sets weren't required to have digital tuning until shortly before the switch from analog. This set may require a digital adapter. If the set does have digital tuning, be sure you have "air" selected and not "cable" for your tuning mode. Also let the set scan for channels.

With digital broadcasting, signal strength is critical. In the analog days, a weak signal would give you a fuzzy picture, but you could see something; with digital, a weak signal means you see nothing at all. You may live in an area where the signal is too weak without using an amplified indoor antenna or putting one on the roof. Your location, other structures around and weather conditions all affect digital reception as well. Many people were (and still are) upset to find that they just couldn't get any channels at all once digital broadcasts took over.

I hope this has been helpful. Thanks for using Fixya!

TV SETTING
1. Press the MENU button.
2. Use or button to select the TV setting menu, then press or button.
3. Use or button to select the Channel no. setting and use the or button
to change from AIR (over-the-air broadcasts) to CABLE (cable/satellite broadcasts).
4. Use or button to select the Tuning mode and use the or button.
5. Use or button to select the Auto tune and press or button to
confirm the selection. The unit will immediately search through all possible TV
channels and store those channels with signals in memory. After this is complete,
the unit will switch to the first channel found.
6. To exit the MAIN MENU and return to the normal screen, press the EXIT button.
Note : In DVD mode, this option is not available.
Remarks:
1. Channel no. : 2-69 channel for Air mode, 1-125 channel for Cable mode.
2. Tuning mode : Air or Cable mode are available.
3. Auto tune : Searches for usable stations and stores them in memory.
4. Skip : ON - Skip weak channels. OFF - No channel skip.
5. Fine tune : The frequency changes to allow fine tuning.
6. AFC : Auto frequency control.
7. MTS : Select the Mono sound/Stereo sound/Secondary Audio Program (SAP).
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TV SETUP
MTS (Multi-channel Television Sound) SETTING
This feature allows reception of sound other than the main audio for the program.
1. Press the MENU button.
2. Use or button to select the TV setting menu, then press or button.
3. Use or button to select MTS menu, and press or button to select the
options (Mono, Stereo, SAP)
4. To exit the MAIN MENU and return to the normal screen, press the EXIT button
on remote control.
Note:
• MTS only operates while in TV mode.
• The SAP (Secondary Audio Programs) feature allows a TV station to broadcast
other information, which could be audio in another language.
RESTORE SETTING
If you reset the TV to the factory settings, all your present settings on picture &
sound will be erased and replaced by the factory’s default settings. However, picture
setting in PC mode and parental setting will not be erased.

1. Since my problem (Samsung/Comcast) began with a channel selection button pushed on the TV remote when it should have been pushed on the cable remote, I figured the problem lay with the TV.  Although I was getting the "weak or no signal" msg., the actual signal strength bar graphic showed it to be strong. Disconnecting did no good. I surmised that the TV was simply not recognizing the box.
2. I looked at the manual for my Samsung 750 model. 
3. Page 20 discussed "Selecting the source". I accessed the TV menu and selected "Input", then chose the "HD..." item from the highlighted list. Voila! My tv works again.