Why is my Mac freezing after memory upgrade?

So I read my MacBook will work with a 16gb ram upgrade. So I tried it. I believe it's the correct ram 1333 1600 and so on. I do think it's a cheapie brand though. Well I installed it rebooted my Mac and it seemed to be working fine, a lot faster then before. But after maybe 15- 20 mins of use it will freeze. Pixelated screen and a loud beeeeeeeeep noise. Can anyone help me out? Is it rejecting the upgrade? I tried the control option r p thing. No luck. It was pretty dirty when I opened it. Could that be it? Or is it simply rejecting the ram?