First, make sure that the keyboard/mouse is connected properly to the PC.
If this is not the issue then contact a member of IT Services (NUIT) Cluster Room Support (CRS) staff. In the Philip Robinson Library there is an IT Service Desk (opening hours may be found here). In the Marjorie Robinson Library Rooms and in the Walton and Law Libraries you should contact NUIT following the instructions here. You will need to state your Newcastle University Campus ID (e.g. B654321), your location and the PC identifier (the number on the PC).
Unfortunately, outside staffed hours you may have to wait until the next day for assistance.