I am also 68 years old and I do not have any professional knowledge about the computer hardware.However when I faced similar problem with my PC with win xp operating system loaded with cleaning soft wears (FREE not paid) my mechanic advised me to increase the memory of PC.He also advised me to replace the HD with higher capacity and if possible upgrade operating system to win 7. I have done that and now there is no problem with my PC,though I have loaded many soft wears which are freely available on Cnet.
So it appears that there is a problem with your PC memory .Also verify that there is sufficient space on C drive.

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