Won't upload MAC OS Snow Leopard

Dear Fellow Apple and Mac Lovers,

I received a notification from my computer that I was unable to sync my iPhone 4S to iTunes. 1) My iTunes needed an update and 2) I could not perform this update without forst upgrading my Computer software to an OS version greater than 10.6.8.

I purchased the Apple software (Mac OS X Snow Leopard v.10.6.3) and attempted to run the software. The computer flat rejected the disc and spit it out of the drive. I uploaded a CD to ensure it wasn't my disc drive and the CD opened and populated into iTunes, ready to transfer the music. I attempted again to load the Snow Leopard onto my computer but it again spit the disc out.

My laptop is a MacBook. MacBook 4,1 (I purchased it in early 2008) Current version 10.5.8. Processir 2.4 GHz Intel Core 2 Duo. Memory 4 GB 667 MHz DDR2 SDRAM (I have NO CLUE what the extra letters mean beyond megahertz) When I perform a software update check it states that the computer does not have any new software for my computer at this time.

I am wondering if I purchased this software for no reason as my computer will not identify software beyond its current update. I am concerned about the computer as I use it for my businesses and have not had the opportunity to replace it with a newer version. I do backup my information on Time Machine regularly onto an external hard drive

I am looking for some clarification if there is anything I can do, or if it is finally time to lay the computer to rest and buy a new one.

All your help is appreciated.

Danielle G