Re addmittion to Uk ,Urgent Enquiry

hi

i have a student visa valid from 30/10/2007 to 31/5/2012. i have completed my stidies at brunel university in Bsc(Hons) Business and Management, i want to continue my further studies at the same university, so i want to go back to uk on 10 september 2010, so i can pay my fees and continue my studies, they have held a place for me their,as i am accepted in the Msc Marketing course,

i wanted to know do i have to apply for the visa again or my old visa is still valid and will i be allowed entry in United Kingdom.

Regards