why can't i add attachments now when I was able to before?

[Nic Brough -Adaptavist-]

An admin changed the permission scheme and excluded you, or changed your group or role memberships so that you no longer match the rules in the scheme.

(Or, on an outside possibility, the server ran out of space, and JIRA disabled the attachments functionality)

In all cases though, you need to talk to your administrators.