Although I tend to use AVG on all my machines, I had a problem a couple of years ago in that AVG made the copy of XP pro on my main machine crash! Remove AVG and the problem went away, so I swopped over to Avast. With this I have had absolutely no problems at all except that it never notifies you that its licence has expired and requires (free) renewal. In Avast this is an annual event, and the first thing you know about it is when XP tells you that your virus software is out of date. This takes a month or two after Avast refuses to update due to the lack of a current licence.
I have never managed to track down the reason for my AVG problem. It does not occurr with any of my other computers which run on XP home or pro. Subsequent software modifications may have by now eliminated the problem anyway. The only possibility is that, at the time, only my main computer was running the software to interface with my networked Netgear remote hard drive backup unit. That software is now running happily on my laptop running on XP home, protected by AVG - which doesn't need its licence renewing annually.
P.P.