I use AVG, CCleaner and Lavasoft Adaware between them they seem to keep me protected, and relatively trouble free, a lot depends on what the grandson downloads as to wether I get any crashes but running the above usually sorts them out. I suppose the fool proof way is to back everything up and do a reinstall of the operating system that makes most systems more stable. Also its worth while running a virus check via Trend Micro house call every month or so.
If you are then still getting problems these guys usually will find a solution
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TREND MICRO HouseCall 6.5