Typing problem

Just bought a new computer with Vista operating system. Sometimes when I
type, letters will not show up and system runs very slow. I have to hit the
letter key sometimes 2, 3 or 4 times for a letter to show up. I happens in
some game rooms and on Yahoo music site when I have a music video playing. I
don't have any problems typing on Microsoft office Word or while I'm typing
this complaint. I have plenty of RAM and Circuit City took off all the stuff
I wouldn't need so the computer would run faster. I've read other people
having the same problem. I'm thinking of taking the computer back and using
my old five year old computer that runs faster. Here's the questions....if I
take the computer back, will people be able to get my personal information
off the hard drive if they sell it and does anyone have a fix for the typing
situation?