unknown operating system after repair

Hello. I have a dell laptop (Latitude D600)running windows xp. I did a system repair with the dell disk. Now when I reboot it gives me a choice of operating systems - windows xp is first then below that is unknown operating system. I click the xp and it loads great. How can I get rid of the choice and also I would like to get rid of the files that the unknown system is using if possible. Thanks so much in advance for any help.

 

I was able to reinstall again and got computer back to normal. Thanks all!