Installed Ubuntu in a old laptop, now it won't boot without the bootable USB stick plugged in
https://askubuntu.com/questions/1568071/installed-ubuntu-in-a-old-laptop-now-it-wont-boot-without-the-bootable-usb-sti
UPDATE:
Eventually the PC stopped booting even with the USB stick, so I decided to try with a booteable USB with w10. It worked, so I debloated w10 and decided to install Linux Mint instead of Ubuntu alognside w10 but I ran into the same problem. I booted with the w10 booteable stick and ran the repair option, which somehow made it so the pc booted directly into Linux Mint with no menu to select OS. That was easily fixed by forcing the menu to appear from the system's options. I really dont fully understand what happened or why my PC broke everytime I tried to install a Linux distro, but it's now working and my mother is using it for work so it's a happy ending. Thank you all for your help and sorry for waisting your time.
First of all, these are the laptop's specs:
Model: SAMSUNG LTD. 300E4A/300E5A/300E7A
Memory: 4 GiB
Processor: Intel Core i5-2450M x 4
Graphics: Intel HD Graphics 3000 (SNB GT2)
Disk: 1 TB HDD
It's old (10+ years) and I wanted to give it a new life just for lightwork. I checked and it is not under the supported hardware for ubuntu, but used the Try Ubuntu feature and it works, so I assume that even if it hasn't been tested to be in the supported devices tab it should work just fine.
The problem:
After the install process I rebooted and the PC asked to remove the bootable device and press enter, so I removed the USB flash drive I used and press enter. Now, when I try to boot the PC, it just gets stuck in a loop, trying to boot up. I can't get into the grub menu by holding down the Shift key. The only thing I can do is boot into BIOS in the Boot settings. I only have the option to change the Boot Priority Order. Another device appear on the list besides the HDD. I already tried changing the priorities, but nothing changes.

If I boot up with the bootable USB connected the grub menu appears without any input from me, and only two options are available: "Try or Install Ubuntu", and "Ubuntu (safe graphics)". The first time I clicked on the first option and just reinstalled the OS but the problem didn't go away. I can close the install window if I boot like that again and use Ubuntu as the Try Ubuntu feature, but nothing more.
I already tried different things I found online in forums, but I don't have the exact same issues or menus/options.
For example,I tried the solution in this forum, but I don't have the add customized boot option in my BIOS.
I also tried this one, but I don't have the Advanced options for Ubuntu on my GRUB menu.
The other thing that I tried was Boot-Repair twice. The first time it have back this link: https://paste.ubuntu.com/p/bpsF9b8Nqh/, and said to share it if the problem persists (which it does), and it also gave me this warning.

The second time I tried using Boot-Repair I got this error message: Glade2script-python3 Is Not Responding.
I screen recorded what happens when I turn on the PC with and without the USB:
Video 1: Booting without bootable USB and getting into BIOS
Video 2: Booting with bootable USB
I'm afraid I've gotten myself into something that's way above my understanding (I never used Linux before).
Edit: Result of sudo fdisk -l
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: SAMSUNG HN-M101M
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: D564C26C-C9BF-49E9-9DC6-3A995C70E836
Device Start End Sectors Size Type
/dev/sda1 2048 4095 2048 1M BIOS boot
/dev/sda2 4096 1953521663 1953517568 931.5G Linux filesystem
Disk /dev/sdb: 14.51 GiB, 15581839360 bytes, 30433280 sectors
Disk model: STORE N GO
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x39ed4277
Device Boot Start End Sectors Size Id Type
/dev/sdb1 * 2048 30433247 30431200 14.5G c W95 FAT32 (LBA)