Puppy
Puppy Linux is also a lightweight distro althought their download pages seem to be offline for maintenance.
@akbimal
When you have two pieces of dissimilar RAM the computer will run at the lowest speed.
The motherboard takes a maximum of Source - https://www.asus.com/us/Motherboards/P5PEVM/specifications/
You need a lightweight distro.
Look at
https://www.techradar.com/news/best-lightweight-linux-distro
https://itsubuntu.com/22-best-lightweight-linux-operating-systems-in-2020/
https://fossbytes.com/best-lightweight-linux-distros/
https://www.blackdown.org/best-lightweight-linux-distros/
Try something like Lubuntu.
NOTE! You cannot install many heavyweight apps on a lightweight distro without weighing it down.
Puppy Linux is also a lightweight distro althought their download pages seem to be offline for maintenance.