cannot reply to emails

Factual Questions
1

I’m using Outlook 2003 and windows XP.
I used to be able to reply to emails by simply clicking the reply button.
The last time I did this was a week or two ago.
Now, when I click reply, a blank window opens, the hourglass comes up and Outlook 2003 stalls. If I close the window, the program not responding comes up and prompts me to close. If I do, Outlook 2003 shuts down.
Any suggestions?