When I withdrew affection from my H around the 3yr mark, it was b/c I was hiding smoking cigarrettes from him (he hated it and I didn't want him to find out) and I resented him for coming home from work, turning on the TV and sitting there the rest of the evening. He never engaged in conversation, never helped with chores or the dogs...I just started to 'check out'.
This led to further complications and As on both of our parts.
Please talk to your wife and try to find out the cause of this sudden lapse of affection. There is something going on. It may be small right now (resentment? stress?) but if it is allowed to snowball, the outcome will not be good.
Maybe she feels you are only using her for sex? Maybe she is really stressed out and not finding the emotional support she needs from you. You may do nice things like make dinner, light candles, get flowers, etc, but if you are not simply listening to her vent and trying to be supportive...that could be the problem right there.
Women need someone who will listen to them as well as support them without trying to "fix" the situation. If you are constantly trying to "fix" her problems instead of just listening, that will start to build resentment. Women don't need problems to be "fixed" - they need problems to be listened to without alot of "Well this is what you should do...." We solve alot of our own problems by talking them out with someone who will simply sit there and listen