outlook 2007 issue

hello,
so i have XP home on my laptop and office 2007. up until last week outlook has been running fine, but now i get an error whenever i open it and cant seem to find a way to fix it. the error i get is: "cannot open your defauly mail folders. an unexpected error has occurred. MAPI was unable to load the information service mspst.dll. Be sure the service is installed and correctly configured."

if anyone could help me solve this issue i would greatly appreciate it.
thanks