Q: upgraded Macbook 5,1 to 8GB system too Slow

Hi ...

Make sure the RAM is seated properly.

MacBook: How to remove or install memory

edit: Carolyn makes a good point ... my comment below assumes you've seated the memory correclty, and the system recognizes it.

Without a lot of drama, put your 2GB back in, and return the memory.  Instead, buy memory from Crucial at http://www.crucial.com or OWC at http://www.macsales.com. Crucial has a memory selector and guarantees their memory will work when chosen from their memory selector. There's usually a 5% off coupon on retailmenot.com and shipping is free. OWC has their own branded memory as well as Samsung and sometimes other brands. I've bought from Crucial for years and Samsung from OWC, and all have worked well.