Either it's a bad stick or it's a good stick that isn't compatible. You'll only know if you try with a PC that's guaranteed to be compatible.
Try again with the memory selector at crucial.com and buy from them.
I was given a computer which is only about 2 or 3 years old.
it had 512mb of ram and i bought a 1gb stick on ebay to upgrade it to put windows 7 on the computer.
I put the 1gb in along with the 512mb and installed windows 7 but the graphics were messed up looking. so i removed the 512mb of ram and only kept the 1gb in the pc and when i turn on the computer i just get a beeping noise.
The ram in the pc was: 512mb PC2-5300-667MHz
The ram I bought is: 1GB 667MHz DDR2 PC2 5300
Any help appreciated.