4 beeps at PC startup work fine

It is an older generation AMI BIOS (2008) but no errors are displayed at startup.

I need to know if it's a long 4 beeps, short... Like here: https://www.commentcamarche.net/faq/7428-bips-du-bios-et-codes-d-erreurs-les-plus-frequents or on the site I posted above.
It could be the graphics card, the RAM, or it could be a motherboard error. Start by testing the RAM, download Memtest86+ version 5.01: http://www.memtest.org/download/5.01/memtest86+-5.01.iso.zip
You will get an .iso file; with Windows 7, right-click on it and Burn, once burned onto a CD or DVD, you will need to boot the PC from the CD/DVD drive (F12 on startup to get into the boot menu and select the DVD drive). Alternatively, you need to enter the BIOS and change the boot order: https://www.commentcamarche.net/faq/7817-modifier-l-ordre-des-peripheriques-de-demarrage
When Memtest prompts you to press F1 or F2, press F2, this will activate all the cores of the processor. Let Memtest run one pass; if there are no red lines appearing, then the RAM is not at fault. However, if there are tons of red lines appearing, there's no need to let Memtest finish, turn off the PC and test each RAM stick to identify which one is problematic; if all are problematic, it’s likely the motherboard that has an issue. If you only have one RAM stick, try with an equivalent RAM stick taken from another PC, or change it.
If the RAM is not the problem, then to test the graphics card, simply launch a good heavy game or a graphics card benchmark with this: https://benchmark.unigine.com/heaven?lang=en
If the graphics card is fine, it could be the motherboard that has an issue. But before testing everything, start by resetting the BIOS to 0 via a CLEAR CMOS. On the motherboard of the PC, there is a battery; next to this battery, there should be a jumper (a piece of metal covered in plastic used to connect two metal pins), it is by default on the right (pins 1 and 2), move it to the left (pins 3 and 2) for 10 seconds and put it back in its normal position. This will reset the BIOS to 0; on restart, it will prompt you to press F1 to continue booting the PC or another key to enter the BIOS, go into the BIOS and reconfigure it.
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Google is your friend.

My motherboard is an MSI Model MS-7309 and there is no jumper on this board to reset the BIOS. As for the memory test, I noticed that I could no longer burn, so I'm checking if my burner’s firmware is up to date, and it is.
I replaced my burner with the same new one and surprisingly, I did a burn test and it worked well.
Now I'm going to burn memtest and, yet another surprise, I still can't burn on the new burner with DVD +RW or DVD -R.
I did a memory test using the Windows utility and there are no issues with the memory.
My graphics card is integrated on the motherboard and it works fine.
So since I was only able to burn once, there is probably a problem with my BIOS.
But how can I reset the BIOS when there is no jumper?

If there is no jumper, simply remove the battery for 10 seconds and then put it back.

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Google is your friend.

I read here: https://www.vulgarisation-informatique.com/bips-bios.php

I now have 3 beeps, and how can I tell if it's for "POST errors" or Boot Block beeps?

Hello,
Normally, Boot Block errors occur when updating the BIOS (if I'm not mistaken), so what we're interested in here are POST errors. Apparently, it's indeed a memory issue. Try removing and reseating them, and clean the contacts with 90°C alcohol if they're dirty. Otherwise, the best way is to test the memory sticks not with the Windows utility (which isn't great) but really with Memtest86+. If you don't have a CD drive (not even USB or on another PC that you could dismantle and connect to this one?), you can put Memtest86+ on a USB stick: https://www.commentcamarche.net/informatique/composants/1437-tester-la-memoire-vive-ram-d-un-ordinateur-avec-memtest86/#tester-depuis-une-cle-usb

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Google is your friend.

I removed the battery again after letting the capacitors discharge all night, removed and cleaned the RAM. Now I have 3 beeps, and I deduce that there is an issue with the RAM despite having done a full test with memtest included in Toutourescue Linux.
Thank you for taking the time.

Hello,
If you have tested your RAM modules with Memtest86+ and no red lines (errors) appeared, your RAM has no issues.

--
Google is your friend.

I just did some research and I was wrong about the Boot Block; the Boot Block is an area of typically 64KB that is generally not directly erasable, and it contains vital BIOS data. The beeps identified as Boot Block beeps are the first beeps you will hear (so before the POST, before any screen display). So if those are indeed Boot Block beeps you hear, it indicates a problem with your BIOS. If Windows starts correctly and the PC is stable, a BIOS update may possibly resolve the issue. BIOS: https://www.msi.com/support/mb/K9N6SGMV__K9N6PGMFI__K9N6PGMF.html#down-bios
Check if this is indeed your motherboard and the correct model (look at the inscription at the top of the motherboard), take exactly the correct BIOS for your motherboard and take the latest version (1.C on the site, IF it is indeed your motherboard). Then download the file; in the file you will also find the instructions for flashing the new BIOS, FOLLOW them to the letter. Do not attempt to update your BIOS using MSI's Live Update (I tested it, it flashed the wrong BIOS; motherboard is now dead). Close all open programs and/or those running in the background, also disable the antivirus (just in case), and start the flashing process (from Windows if you can, or from the BIOS; follow what is written in the instructions). If the update does not resolve the issue, look on the motherboard to see if the BIOS is directly soldered to the motherboard or if you can remove it. If you can remove it, we can try to find exactly the same BIOS on the internet; otherwise, you may need to replace the motherboard. But if the PC is functioning for now, we'll say that it's okay.
Google is your friend.

I will first set up another PC and then I will test it.