I just had to install a new internal hard drive because the old one crashed. I have a Macbook 4.1 (Penryn) EMC 2242. I am trying to install the OS system. I have a Snow Leopard install DVD but it will not install. Help???

See if you can "burn" the Snow Leopard DVD installer to a USB drive using these instrucitons:

https://www.maketecheasier.com/create-mac-snow-leopard-usb-installer-disk/

If you are using a more recent version of macOS, then instead of creating a new partition on the USB drive you just need to erase it as GUID partition and MacOS Extended (Journaled). The Restore process is also a bit different than that shown in the article, but you should just be able to highlight the mounted SL DVD on the left pane of Disk Utility and click the Restore tab. Then select the properly formatted USB drive for the destination.

Then Option Boot the SL USB drive by holding down the Option key just after the startup chime so you access the Apple boot picker menu. The SL USB drive will be the orange icon.

If this doesn't work, then you need to try my other previous suggestions to see if you can narrow down where the problem may be.

Hello,

Which error message are you receiving when you attempt to install macOS? Your Macintosh’s hard disk may be failing.

The Leopard installer won't work since it is the install disc which shipped with a different model computer. If you have a Retail copy of Snow Leopard, then you should be Ok. If this is just an "upgrade" version, then perhaps it requires a copy of an older version of macOS before it will install. I don't recall much about the earlier upgrade DVDs. See if there are any installation instruction documents on the Snow Leopard DVD.

What drive did you install in this laptop? Just because the drive is new doesn't mean it is good or compatible. Hard drive technology has changed a bit and new hard drives or SSDs may not always be compatible in such an old system.

Maybe the problem is with your DVD drive or perhaps there is a problem with the DVD itself. Try using an external USB DVD drive.

It should be possible to make a bootable macOS Snow Leopard USB installer from the DVD installer. I'm not sure if it is as simple as using Disk Utility Restore or not (or using "dd" to copy the DVD to a USB drive). I recall seeing instructions online years ago, but don't recall the specifics.

To make sure the DVD drive and your new hard drive are working correctly you can try installing Linux on the laptop. Kubuntu, Ubuntu-Mate, or Linux Mint are all good choices as they should be very easy to install on this laptop although they may run slow if you only have 2GB of RAM. If you can install Linux, then it should indicate everything is working and the problem is due to the Snow Leopard DVD or DVD drive itself. If you burn a CD for the Linux installer, just know that a CD may work when a DVD may fail since they use different frequencies for the laser to read the discs. You can "burn" the Linux installers to a USB drive using Etcher (Mac/Windows/Linux).