I bought a Western digital hard drive for my laptop (hp 510) its a 120 gb and it wont load y?

I turn on my computer it works fine, it does the windows loading but after that i get that annoying blue screen telling you to restart due an error. the computer knows the hard drive is there but why doesn't it work i did the setup windows( f10 main screen) i did a memory check. i kow i put it in right. so what do i do?