Can anyone help me with vista??? plz?

i had windows vista business in C:\ which is my primary drive, but now i m using windows 7 in D:\ for 2 months. but 2day when i tried starting vista its showing that its been expired and not allowing me to enter the OS, so nw how can i remove vista frm C:\ and make D:\ my primary drive, bcoz when i try it it doesn't allow me to do bcoz of being C:\ my primary drive. so plz hlp me out...