A laptop from 2012 would perform better with a lighter flavour from the Ubuntu family such as Lubuntu or Xubuntu.
Secondly, for pre-UEFI PCs, there have been occasions where the OS may need to be installed on one partition only i.e. without the BIOS Boot partition ( yours is sda1)
Have a look at this example (post 6) https://discourse.ubuntu.com/t/operation-system-not-found-dell-inspiron-n4110/51073/5
Lastly, ensure that you have backed up your personal data.