If you are having trouble, this will explain it to you. There are two types of login problems:
1) You had an account before and now the pass doesn't work. If this is your problem, try using only the first two characters of your password and then login. It will display an error as explained in (2), but don't worry. Read problem (2) and then change your password back to what it used to be or even a new one.
2) You try to log in but it displays a "Page cannot be displayed" (404) error. No worries, just go back to the forum and refresh and then you'll be logged in. I don't honestly know why it's erroring, but it doesn't seem to be a fatal problem.