For no apparent reason, system freezes for several seconds to a minute, then
unfreezes, may happen again in several minutes or just a few minutes, or not
again for a day. My attempts to restart or turn off also fail and error
"Shelllcom hidden window" appears when trying to reboot or turn off. I've
done everything such as scan for viruses, adware, spyware, etc. I've run
disc cleanup and defrag, etrc. What else can I do?