error in connecting database

hie guyz
i have problem in connecting service based database in windows forms.
when i click it its shows me the error
connections to sql server database require sql server 2005expres or 2008 express to be installed and running in the local computer
i dont know how to solve this error i have installed sql server2010 express from the website
but the error is not going
i am using windows 7.
but when installing whole package of vs2010 in windows xp doesent gives me such error only in windows 7 i am facing this problem