Do you have an e-mail notification regarding a password change? If not, I'd guess that your problem may be linked to Guild Wars 2. If you have linked your original Guild Wars account to gw2, the password will be the same used in gw2. I believe there may be a slight delay following the first time the two are linked. Still I suggest you treat this as a security risk and notify Anet. These are merely proactive steps that may or may not help (seeing as a reply from anet will likely take a day or two).