Imac 2008 issue need help

I have a late 2008 24 inch iMac. Last year I upgraded to double the ram from 2gb to 4gb. I think this messed up the computer after 8 months. I just took reinstalled the original ram and it's working now. Before all that would happen is it would take forever to start up and then just keep loading. This has been fixed but now when I dump stuff in the trash nothing shows up. I go to the trash and it has a ?? mark.

Do I need to get a new HD or just update/full reboot the system. I lost the original install disk. If I download the latest OS can I reboot to factory settings?

 

So looking more into it it's a mid 2007 iMac

The HD is fried. When I tried to reinstall OS Snow Leopard on it says SMART error which is basically your HD is dead and get a new one.

Has anyone ever changed a HD on these things? Youtube says it take an hour to do and is a 3/5 in difficulty. Thing is already dead and I haven't tinkered with the inside of my computer since I stop buying PCs 10 years ago.

Anyone know how much I can get for this .... would be good to at least be able to get a ipad for this baby.

Sucks its a great little computer I wanted to give to my niece once I got it up and running but I guess it is not meant to be.