New RAM install now Mac not restarting

Hi All

Pretty new to upgrading macs (was formerly a PC person) so I have a question regarding an upgrade I want to do on my Mac Aluminium Uni body. Currently running with the stock 2 gigabyte RAM but I wanted to bring it up with the 4 - so I bought a stick of 4 gigabyte (PC 3-8500) - which I believe is correct. So why is it when I install it, I just get a series of beeps (3 fast, than 3 slow) and nothing or a grey screen? I've tried holding Command, Option, P, and R and that doesn't do anything either (is it a timing thing? Do I do it after the grey screen appears?). I thought maybe I fried the logic board, but when I put the original ram back in everything boots up fine.

Am I missing something? Do I have to have BOTH slots filled in order for it to boot? Should I have gone with 2, 2 gigabyte instead of one 4?

I've searched the Google and the existing forums for this, but I can't find things that deal with what to do if you can't get the reset to work.

Is this just bad ram?

Please accept my apologies if this has been addressed and I haven't found the thread (in which case feel free to link it for me)

Current set-up:

Late 2008 Mac Book Uni Body 2.0 processor

no peripherals

2 gigabytes ram

160 g hard drive

What ever it had in the box, this is the first upgrade I've tried

Running on mavericks