I don't know 2000 well, so I don't know if this is version-specific, though I doubt it. I can think of three things to check:

1. Does the text you are trying to copy and paste has a fine dotted underline? If so, it is probably "hidden text" and won't copy. You can select it, go to font properties, and uncheck "Hidden text", unless

2. The document is password protected, in which case you will need the password to unprotect it.

3. If neither of those is the cause, perhaps either your Normal template has been boggled up somehow, or Word itself is. I don't think 2000 has a repair function in the menus, though it may, under Help or Tools. If not, and if you have the installation CD, you may try running repair from that.