DDR3 RAM upgrade issue

Hi there,

Thanks to all of you in advance, this may have been brought up elsewhere but I haven't found a straight forward solution to the problem.

I have been running a HP compaq 500B with Win7 and only 1GB RAM. Extra RAM is not so easy to get here in Kenya but today I finally managed to get an extra 2GB DDR3 Ram stick today for around 65$ (some of you may laugh, I do not!)
Now I have never done this before but I thought all I have to do is plug the thing and it will work, and it actually did, for about 20 min I was pleasantly impressed by the refreshing speed of my machine until I got a blue screen. Once I restarted I got a couple of more blue screens and system errors, so I decided to remove the old 1GB RAM stick and leave only the new 2GB. Things only got worse, my kaspersky antivirus wouldn't find its database, more blue screens, etc...

No I am back in slow motion on my 1GB RAM, I don't know what is wrong, both sticks are PC3 10600 DDR 3 Ram and therefore compatible, right?
And if not at least the better 2GB should work, no?
Is there maybe something really simple I am overlooking?

I would really appreciate any hints, thank you again in advance!

Sounds as if you may have purchased a faulty ram stick. If computer gives errors with the stick in and runs good with the stick out, you have a bad piece of memory.