How do I diagnose my issue, when I'm not sure if it is a hardware or software issue?

I’m having some issue. I’m not sure if it is a hardware issue or a software issue, but I’d like to determine the cause of the issue so I can fix it. How can I do that?

>Solution :

It’s pretty easy. Take a USB stick. I suggest 32 GB, but other sizes work too. Make a backup of everything important on this USB stick, because we will put a live CD on it.

There are a few possible solutions from here. Pick the correct path depending on what the issue is.

Creating a Ubuntu LiveCD

This isn’t a troubleshooting step on its own, but I mention it several times, so I’m having it be separate.

1. Download the latest (not LTS, and not experimental, but latest and supported) release of Ubuntu Desktop from the Ubuntu website.
2. Verify your download. You don’t have to, but I suggest it, especially if your internet connection isn’t great. Follow the steps on the Ubuntu Wiki.
3. Next, you need to write the ISO to the flash drive. You can use dd, but because it is easy to mess up, I suggest
   balenaEtcher instead (no affiliation, but I like it). Download the
   Linux 64 bit version. Open a terminal, and navigate to where the
   downloaded .zip is (probably ~/Downloads). Unzip the .zip file with unzip balena-etcher-electron-X.Y.Z-linux-x64.zip. Make the AppImage inside the .zip executable with chmod +x balenaEtcher-X.Y.Z-x64.AppImage. Run it with ./balenaEtcher-X.Y.Z-x64.AppImage.
4. Select the ISO, your flash drive, and hit Flash!. Wait for it to finish, and reboot to your flash drive.

I think the memory/RAM is bad

1. Download MemTest86.
2. Open balenaEtcher. Select the ISO you downloaded from step #1, and the USB stick. This is your last chance to backup any data on the flash drive before it is gone forever. Press Flash!. Wait for it to finish and verify.

Note: You can skip the above steps if you are on a dell based hardware. Dell laptops already include MemTest86 by default.

3. Reboot your PC, and boot to the USB stick (in the boot menu, select the flash drive).
4. Run a memory test. If it fails, you have a memory issue. Replace the bad stick(s) of RAM.

I think my disk had an issue

You can either do this from a live CD (see above) or from your main system. For an HDD, check the SMART data. See here for how to interpret those numbers. If you have an SSD, you can still try to check the SMART data like an HDD, but you can also check the wear indicator (a measurement of how worn-out your SSD is). For that, see this answer.

Why doesn’t XYZ hardware work?

First, check the obvious (is it plugged in)? Don’t go through this entire process to realize you plugged your USB stick into an Ethernet port. Yes, it happens.

Done that? OK. Create a Ubuntu Live CD with the latest release version of Ubuntu. Not LTS, the latest release. See the directions above. Boot to it, and press Try Ubuntu. Now, try to reproduce the issue or see if "it works". If it does, yay. Upgrade to that version of Ubuntu (after taking a backup), and it should work. Done. If it doesn’t, search online to see if anyone else has. If not, check out the output of dmesg, and see if there is anything relevant there. Also, you can try making a live CD with the latest beta version of Ubuntu, but that isn’t stable, so I wouldn’t suggest it unless you know what you’re doing. Of course, feel free to ask a question here. Remember to provide your OS details (version, etc.), and what you’ve tried. Not everything works with Ubuntu, so you might be out of luck.