Help with logging in to MacBook Pro.

I Got a MacBook Pro today and i was abler to log in fine. But when I changed the password to something personal to me so no one could get in it, after entering it, I wAsnt able to log in. So I put in the installation disk and reset everything and changed the password. It let me in..but the applications were gone. So I put in the application disk and it uploaded that. But then, they still didn't work. it said that the current version of mac osx was not compatible for the apps. so I preceded to do a software update. so that finished, and now I'm back to my problem of not being able to login, I tried resetting it but nothing works. Please help I want to play on my new laptop! Thank you in advance for any advice