As indicated above, if your temp space is stuffed or trashed, you can't copy because there's no place to put it. This usually means that your main hard drive is full, fragmented, or has picked up some errors in the file tables.

Any key combination, like Ctl-C/Ctl-V, right clicking a selection, etc can be redifined to use different keys, or some other operation can be changed to use the keys you think will do the copy/paste. Very rarely a new program may "set" quick-keys that conflict/override the normal ones.

Using the menu bar and clicking down through Edit|Copy etc is almost infallible if the clipboard is functional, so a first check using that method probably would tell whether you have a setup problem or if Windows actually is "broken." The main menu bar can be changed (in versions prior to Vista) but it's rather difficult to make an existing standard function quit working.

(The superior reliability of the bar probably explains why Microsoft removed/hid it in the default configuration for IE7 and why mostly it's trashed/inoperable/useless/non-confurable in Vista - and in new Office programs - generally.)

John