unable to download OS X Yosemite 10.10

Hey there, i have just purchased a 2008 iMac and when turn it on it comes up with the OS X Utilities and i click reinstall Yosemite and then i sign into my apple account and a notification immediately pops up saying this item is no longer available, now i googled this and a bunch of things came up, such as erase the hard drive and i did that, but still the same thing, please please help 🙂