"paste" function failure

I am running Windows XP Home Edition and Office 2003 Pro.
The copy function works, because the copied text shows on
the clipboard. But to copy anything from outside MS Word
to a MS Word document, the "paste" function does not
complete the job and MS Word freezes up, with the hour
glass displayed until I exit from MS Word.

I never had any problem with the "copy and paste"
functions until a week ago, when the completion of
the "paste" began to be agonizingly slow. Yesterday,
the "paste" function ceased to function at all for
any "copy" except within and among MS Word documents.

Help desperately needed. Thanks.