Can't log in?
If you can no longer login to a PC that you used to be able to then the most likely cause is that you have exceeded your disk quota. There are 2 ways to check this:
1. get a friend to login to your computer. If they succeed the problem is your quota
2. Try to login to another computer (ideally one that you have seen in use). If you cannot login then the problem is you.
Assuming the issue is quota then although the graphical login fails you can still either ssh in from a personal device or attempt a command line login from the computer that you are sat at. If you are unable to do either of these things then please contact the IT team.
Password is rejected
If you are sitting at a Maths computer, make sure there isn't a spurious space before your username as this will prevent you logging in. Remember that for most people your Maths account is your crsid (never your email address)
If you have left the CMS and your password has suddenly stopped working, we have probably disabled your account. Email help@maths explaining why you need it reinstated. To avoid this problem, let us know whether you want to keep your account before you leave, and if so, how long you will be needing it for.
Not authorised to login
Either you are trying to log into a machine which is neither public-access nor in your group, or if you are no longer at the CMS, your access may have been restricted to ssh.maths only. Email help@maths who can easily supply you with access to the machine on your desk.