Why since I load Windows Vista, I can't sign in in yahoo messenger, but the e mail...?

I think something is blocking it but what? Is there anybody who knows about this? I mean I sign in in my msn messenger, in my e mail from msn , in my yahoo mail, but in the messenger...please, help me with that

Thanks

Why since I load Windows Vista, I can't sign in in yahoo messenger, but the e mail...?microsoft downloads

it's probably your firewall blocking you - check your firewall settings first and always, I'm almost positive that's your issue