My Systems Restore says it can't restore to dates I've tried. What could the problem be?

[AWS]

I was playing Easter Solitaire when my XP screen turned blue with the notice a serious error had occurred. One remedy suggested was removing any software recently installed which was AVG Linkscanner and then use Systems Restore which I tried using two
different dates both of which brought the response that Systems Restore could not restore to either date. What would prevent Systems Restore from working?

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