Well for the NickServ problem, I can only think of three (four if you count IRCop interventions) reasons you get that problem.
The common reasons:
If you registered the nickname and you get that error saying that it's the password your using is incorrect, it could mean your typing it in wrong, remember passwords are case sensitive on most servers (so the Password "HiGhEr" is different from "higher"). Another reason could be because you haven't been online for a while (normally between 21 - 30 days) and your nickname was dropped by services for inactivity. Someone else then came along and claimed your nickname.
Now for more uncommon reasons:
You came on to a Server with your nickname and it already being used by another person. The last reason I can think of is by some
IRCop dropping your nickname or changing your password, most likely because on a action on your part or (more likely) they were tricked by someone claiming to be you.
As for the giving voice, you can use /mode #channel +v nickname
it should work if your a op on that channel.