given that you did not make changes to SPM or MATLAB, this is most likely not an SPM-specific problem. Within the scope of MATLAB it might be caused by newly installed 3rd party MATLAB code that somehow interacts with SPM, e.g. by replacing SPM or MATLAB functions with new code. Outside the scope of MATLAB, you should look at other programs consuming CPU or memory and any kind of technical problems (RAM, harddisk, network storage if applicable).
Hope this helps,