speed and connectivity

my browsing has slowed suddenly and dramatically and shutting down the computer also takes a long time. It is accompanied by messages that say "waiting for background program to close" (every time) and "preparing to reconfigure windows" (about every three times). on start up, I get "chrome did not shut down correctly".  I had trouble writing this. It was difficult to move the cursor at times and the window disappeared for several seconds during one attempt. The only thing that preceded my problems was the running of, ironically, a Quick Scan, which showed nothing amiss, and the installation of Windows Essentials. A second scan somehow got started and froze early on. One last point: the computer makes sounds as though it is actively doing something, even when I am not, but I can find no mysterious program listed or running anywhere. I'd appreciate hearing from anyone who may know what is going on and how I can correct it.