mac os x installation problem

How did you create the bootable macOS 10.11 El Capitan USB stick?

And exactly what happens when you try to boot the El Capitan USB installer? At what point does it fail and what is the exact error message?

The only reliable method of creating a bootable macOS USB installer is by using the instructions in the following Apple article:

Create a bootable installer for macOS - Apple Support

These instructions require using another Mac which is compatible with macOS 10.11 which is generally one from 2007 to 2015 (the Mac can be currently running any OS from 10.6+). You can use the information in the following article to identify which exact Mac models are compatible with various versions of macOS.

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

Another option would be to use your OS X 10.6 Snow Leopard upgrade DVD to install Snow Leopard. Then you can install macOS 10.11.

Unfortunately troubleshooting Lion installation is tricky because it is so old. How are you even accessing the Lion installer? If this laptop only ever had macOS 10.7 Lion installed or this was the last OS installed when the drive was wiped, then you would be accessing a very old copy of it which would have an expired certificate. The system date may need to be changed to an earlier date such as 2020 or 2017.

Or the error may be indicating a hardware issue of some sort....most likely with a worn out or even failing hard drive (not surprising for a system this old). You can try running the Apple Hardware Test to see if any hardware issues are detected. You will need to boot from the 2nd DVD which originally shipped with this laptop from the factory to boot the Apple Hardware Test.