It sounds like your password has expired. It expires after 180 days and you should have received email reminders to your LSBU email address.
You can reset your password at: go.lsbu.ac.uk/password - just type this into the address bar of an internet browser or copy and paste it.
If you require any further assistance, you can contact us by email: firstname.lastname@example.org or by phone: 020 7815 6678. Please include your student ID number in any correspondence. You can view the Student IT Support webpages and you can also visit our help desk on 1 West, Perry Library.