Windows takes a long time to shut down

I have a Toshiba Satellite C655 running Windows 7 64 bit. A week and a half ago it started taking over a minute to shut down. It started around the time I installed optional updates for Microsoft Security Essentials, my anti-virus program. I uninstalled it, shut the computer down and it still takes over a minute to shut down. Went into safe mode and reinistalled it there, still took over a minute...