Contacts always off line

I've had messanger for some time.. Always worked perfectly. However over the last week ALL my contacts are permanently '' not active'' and it doesn't show the last time they were active either. I've even checked with a friend who I was talking to on messanger to see if she had her status as active.. It was.. But to me she's not active! I've uninstalled and reinstalled to no avail. Pls help! Thanks.