2 Same laptops behave differently. What could possible be wrong?

I am having 2 dell vostro 1550. I setup one of them with ubuntu- 14.04 64 bit. Everything goes well, except after installation when i suspended, It didnt resume and have to hard shutdown.

Now I got the hard-disk switched with another similar system and everything is working fine even the suspend resume is working normal. What could possibly be wrong with the first system?