New copy of pse 18 has all the memory glitches

I lost my faithful PSE7 when my computer died. Bought a new PC - 1000 gb hard drive 4gb memory. Just bought PSE18 on disc loaded it but it wont work properly error messages about not enough memory and simply crashing on several commands. Uninstalled it and downloaded "latest version" exactly the same problems. searched net find many references requiring fiddling with registry. tried that - no improvement but instructions not very friendly. Where can I find a simple solution or how do I get my money back?